Hi Fi Writer - Dictionary of Home Entertainment

A Dictionary of Home Entertainment Terms

Last updated 18 June 2006

This is a practical Dictionary of Home Entertainment terms. The idea is to allow you to find not just the raw meaning of a term, but what it means in real life.

You may find it convenient to link to specific definitions contained here from your own Web site. There is a link to each specific term immediately after the term (right click on 'link' and select 'Copy Shortcut' from the context menu).

If there are other useful terms you would like to see defined or explained, or you wish to dispute a definition or correct some error, email me at scdawson at hifi-writer.com.

This dictionary has nearly 400 entries.

1 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

1080i link: A video display standard, where there are 1,080 visible lines delivered in interlaced format. It is one of the standards permitted in Australia to be regarded as HDTV.
1/4" jack link: See 6.25mm jack.
16:9 link: The aspect ratio of a widescreen TV, in which the height of the screen is nine sixteenths of its width. Sometimes expressed as 1.78:1 (~16/9).
16:9 enhanced link: A picture format used for widescreen movies on DVD. See anamorphic for a full explanation.
1.85:1 link: One of the most common aspect ratios of cinema films, and consequently of DVDs. This leaves substantial black bands at the top on bottom of the display on a standard 4:3 TV, but matches quite nicely with the 1.78:1 aspect ratio of a 16:9 widescreen TV. On such a TV, even the expected thin black bands at the top and bottom of the display are often missing, due to the TV's overscan.
1/8" plug link: See 3.5mm plug.
2.35:1 link: One of the most common aspect ratios of cinema films, and consequently of DVDs. This leaves very wide black bands at the top on bottom of the display on a standard 4:3 TV, and significant black bands even on the 1.78:1 aspect ratio of a 16:9 widescreen TV.
2.5-way loudspeakers link: A loudspeaker which divides the incoming signal into three different frequency bands for distribution to drivers, but in a different way to three-way speakers. It sends high frequencies to the tweeter in the usual way, and low frequencies to one or more woofers. But it sends the midrange frequencies and the low frequencies to an additional bass/midrange driver in the same way as is done in a two-way speaker. In other words, all but one of the large drivers handle bass only, while the last handles both bass and midrange.
3:2 pulldown link: The method used in the NTSC video system for converting the 24 frames per second of film to the 30 frames per second the video system requires. See here for more.
3.5mm plug link: Or 1/8" plug. Often used on portable headphones and playback equipment. They tend to offer relatively unreliable connections due to the very small contact area within the socket.
4:3 link: The aspect ratio of a standard TV, in which the height of the screen is three quarters of its width.
480i link: A video display standard, where there are 480 visible lines delivered in interlaced format. When delivered in analogue format, it is identical to NTSC.
480p link: A video display standard, where there are 480 visible lines delivered in progressive format.
5.1 link: The number of channels of audio in a modern movie. The '5' refers to full range channels: moving clockwise, left front, centre front, right front, right surround and left surround. In Dolby Digital, DTS and MPEG 5.1 formats, each of these five channels is capable of a frequency response covering the full audible range (up to 20,000 hertz). The '0.1' refers to the LFE channel, which is not full range but designed to cover up to 120 hertz, thus the decimal point.
576i link: A video display standard, where there are 576 visible lines delivered in interlaced format. When delivered in analogue format, it is identical to PAL and is Australia's picture delivery standard for SDTV.
576p link: A video display standard, where there are 576 visible lines delivered in progressive format. It is one of the standards permitted in Australia to be regarded as HDTV, although in reality it offers no more resolution than 576i.
6.1 link: An enhancement of the 5.1 channel surround system, versions of this appear in both Dolby Digital and DTS. The Dolby Digital version is called Dolby Digital EX 6.1 while the DTS version appears as either DTS ES 6.1 Discrete or DTS ES 6.1 Matrix. The additional channel is intended to sit at the rear of the room (although two speakers are recommended, even though the same signal is provided to both). This provides a greater localisation of sounds from the centre rear. This is a very useful enhancement in cinemas where much of the audience are sitting off-centre, but in normal rooms with a small number of viewers, it is much less important.
6.25mm jack link: Or 1/4" jack. Familiar from the larger type of headphone jacks (or plugs), these are widely used in professional audio as well. They come in both mono (two conductors) and stereo (three conductors) versions. The latter type are often termed in pro-audio as TRS jacks, and in which application they are often wired for balanced mono operation.
720p link: A video display standard, where there are 720 visible lines delivered in progressive format. It is one of the standards permitted in Australia to be regarded as HDTV.
A/V link: Audio/Visual, as in A/V connections. Most modern TVs have separate sockets for the composite video signal (that's the yellow one) and sound (black or white, or red and white if stereo).
AC-3 link: AC-3 is the encoding scheme used in Dolby Digital, the name by which it is now more commonly known.
AC link: Alternating Current. An electric current that reverses direction regularly. More generally, AC is also used to describe voltage sources in which the polarity of the signal reverses regularly. Power distribution networks use AC because it is relatively easy and cheap to alter the voltage (using transformers) yielding considerable economies for long distance power transmission. All the counties in the world use, it seems, either a 50 or 60 hertz frequency for their power systems. Europe, Australia and India use 50 hertz. The Americas and Japan use 60 hertz. Compare with DC.
Academy aspect ratio link: 1.37:1, the aspect ratio for movies used almost exclusively up to the early 1950s.
Academy sound link: Fairly soon after the introduction of talkies in the late 1920s, the movie industry settled on using an analogue optical soundtrack on the edge of the film to carry the sound. This was read by the projector and converted to an electrical audio signal. This was a very noisy medium, so in the absence of advanced noise reduction technology such as Dolby A (the cinema equivalent of, and precursor to, the Dolby B and C noise reduction systems on compact cassettes), the situation was eased by sharply cutting the treble response (at around 5kHz). The bass was also cut, which accounts for the characteristic pinched sound of old movies. The recommended system of frequency response tailoring was called 'Academy Sound'.
Acoustic suspension link: A design for the enclosure of a loudspeaker. With acoustic suspension speakers the enclosure is sealed so that it is air tight, which causes the air within to become a very active part of the woofer's suspension. This raises the resonant frequency of the driver and lowers its compliance. Acoustic suspension speakers tend to be less efficient than bass reflex designs, and begin fading away their bass at a higher frequency. But the rate at which the bass output reduces tends to be less than an equivalent bass reflex speaker, so they frequently produce greater bass extension. Also called infinite baffle.
Active loudspeaker link: A loudspeaker with built-in amplification for all the drivers. Some speakers have an amplifier built-in for bass only, but these are not regarded as active. Most loudspeakers are passive, not active.
Active subwoofer link: A subwoofer with built-in amplification. Most subwoofers are active, not passive.
ADC link: Analogue to Digital Converter. A component, circuit or device that converts an analogue signal to a digital one, usually to some form of PCM. Compare DAC which does the reverse.
AES/EBU link: Audio Engineering Society/European Broadcasting Union. A digital audio communication standard most commonly seen in professional audio applications. Electrically it is only subtly different to the consumer-oriented S/PDIF standard, the main variation being a different method of handling the clocking signal, and it generally being carried by balanced connections. Nevertheless implementations are seen that seem to be fully compatible with unbalanced S/PDIF.
AM link: Amplitude Modulation. A method of impressing a signal onto a sine wave for its transmission or storage. A constant frequency sine wave has its amplitude increased or decreased from moment to moment to correspond with the signal. The sine wave, called a carrier, must be of considerably high frequency than any component of the signal. AM radio is an application of this technique. Very simple AM receivers (consisting of little other than a crystal and a coil) can be implemented very easily to receive these signals, although of course more sophisticated circuits can produce higher quality results.
Amp link: Short for ampere, or for amplifier. In the former sense, the amp is a unit of electrical current. Amps equal volts divided by resistance (or impedance) in ohms.
Amplifier link: A component or module of a component that increases the amplitude of an electrical signal. Voltage amplifiers and current amplifiers are optimised to provide amplification for specific purposes. See also power amplifiers and preamplifiers.
Amplitude link: The level of an electrical signal, usually measured in volts.
Analogue link: As in not digital. An analogue signal in an electrical facsimile of the item being represented. For example, when playing a stereo DVD, the analogue audio outputs of a DVD player trace an electrical curve that is identical, other than in sheer power, to the electrical curve that the amplifier will deliver to the speakers and this, in turn, is identical to the pattern of sound waves the speaker will create, except for distortions that creep into the system. An analogue signal can have any value within set limit, while a digital signal is constrained to a set of discrete values.
Anamorphic link: Also known as '16:9 enhanced' or 'widescreen enhanced'. This means stretching a picture out of shape, making the images tall and skinny. Many widescreen movies have been filmed on standard Academy aspect ratio cameras and film stock. This can be done either by wasting a lot of film between each frame, or making use of the full frame by using an anamorphic lens to horizontally squeeze the picture together. If a single frame is looked at, the characters will be as mentioned. When the film is shown, a reverse form of the anamorphic lens widens the picture again so that everything appears as it should. On DVDs an anamorphic widescreen picture is encoded to use all the vertical lines of resolution available (576 for PAL and 480 for NTSC). When played back on a widescreen TV it is horizontally stretched so that the picture contents are shaped normally, but with the benefit of DVD's full resolution. If played back on a 4:3 TV (that does not have a widescreen mode), the DVD player's set up menu must be told so that the DVD player can convert the anamorphic picture to a letterboxed picture for the TV. More.
ANSI lumens link: American National Standards Institute lumens. A measure of brightness for projectors under standards set by this body. This specifies an average brightness produced on a screen of known reflectivity using a particular test image, or images. A specification war is underway with each projector claiming a higher and higher ANSI lumens rating. The amount of brightness required for a good job from a projector requires three things to be taken into account, in order of increasing importance: the reflectivity of the projection surface, the size of the projected image, and the amount of ambient light in the room. High output projectors (> 1,000 ANSI lumens) are important for making presentations, class room work and the like. But for home theatre use, look for something lower, preferably under 700. It will generally give you a longer lamp life and darker black areas, which are more important for delivering a good quality image. If the projector has an 'economy mode', try using this. If it doesn't throw out the colour balance too much, it may well deliver a better home theatre image.
Anti-skating link: A device on a turntable's tonearm to counteract skating. This sometimes consists of an adjustable spring-loaded device near the tonearm's pivot, but is better implemented as a weight on a string (since the torque applied by this arrangement remains constant throughout the range of travel).
Aperture grille link: A part of a CRT TV tube. This is a barrier within the tube, placed between the electron guns at the narrow end and the phosphor screen at the wide end. It consists of a series of vertical wires or fine slats. The geometric arrangement permits the electrons emitted for each colour gun to activate only its matching colour phosphors. This alternative to the shadow mask was developed by Sony and marketed under the name 'Trinitron'.
Aspect ratio link: The width of the screen as a ratio of its height. A standard TV screen is four units wide to three high, so is described as 4:3 or 1.33:1. A widescreen TV has an aspect ratio of 16:9 or about 1.78:1. Widescreen cinema movies are typically 1.85:1 or 2.35:1.
ATRAC link: A system for compressing digital audio using perceptual encoding techniques. This was developed by Sony to allow the full contents of a CD to fit onto a Minidisc, which offers considerably less storage space. In recent years a new version, called ATRAC3, has been introduced which permits greater levels of compression than the original version. This permits ATRAC-based solid state players. The bit rates used by ATRAC3 are 132 and 66 kb/s. The ATRAC compression system also forms the basis of Sony's cinema sound system SDDS.
Audiophile link: A person who places, or would like to place if circumstances permitted, a high priority on having an audio system that performs very highly. They have generally trained themselves to be very discerning about the sound of audio systems. Some audiophiles stray into a purely subjective realm.
A-weighting link: A system of adjusting signal to noise ratio measurements to take into account the differing sensitivity of the human ear to different frequencies. Thus an A-weighted signal to noise ratio more accurately reflects how a system's noise performance will be perceived than an unweighted measure.
Baffle link: A plate surrounding a driver in a loudspeaker. The lower the frequency of the sound produced by the vibrating cone of a driver, the more apt it is to simply cause air to rush from one side of the cone to the other, rather than produce the compression waves that constitute sound. By adding a baffle around the driver, this increases the length of the path that air must travel, lowering the frequency at which this destructive interference takes place. In most loudspeakers, the enclosure forms a baffle. In the case of infinite baffle enclosures, the enclosure is sealed (thus 'infinite') while with bass reflex speakers a port is carefully tuned to allow energy from the back of the cone to supplement that from the front at selected bass frequencies. In regular talk, the baffle is the front panel of the loudspeaker.
Balanced link: An electrical circuit in which both the signal leads (positive and negative, active and neutral or whatever) carry equal but inverse signals produced by the source. These require three conductors: two for the signal plus a separate one for the shielding. Balanced connections are fairly rare in consumer electronics, although they are provided in some high-end equipment. Well-designed balanced circuits provide excellent rejection of electrical interference generated in connecting wires. Balanced connections frequently use XLR plugs and sockets.
Band pass filter link: An electrical circuit that only permits signals between two particular frequencies to pass through. An example is section of a crossover network that allows only the middle frequencies to be delivered to the midrange driver. Compare low pass filter and high pass filter.
Bandwidth link: Either the range of frequencies which a component can deal with competently (often specified as the range across which the attenuation is no more than 3dB), or the frequency range required to carry a signal. For example, the bandwidth required for a composite video signal is somewhat more than 5MHz.
Bass link: Low frequency sounds, typically below around 150 hertz, although the dividing line between bass and midrange is one of opinion. The human ear is less sensitive to bass than to midrange.
Bass extension link: An imprecise term concerning how low in frequency a loudspeaker or subwoofer can still operate to produce usable output. A typical bookshelf-sized speaker may manage a bass extension of 80 hertz (say, at -10dB), a good floorstanding speaker may manage 30 or 40 hertz, an inexpensive subwoofer 40 hertz, a middling one 25 to 30 hertz, an expensive one 16 hertz.
Bass management link: A facility in home theatre receivers that permits some of the speakers in a 5.1 channel system to be specified as 'small' rather than 'large'. 'Large' speakers receive the entire signal for their respective channel, but 'small' speakers have the bass stripped off and sent elsewhere. If a subwoofer is attached, this bass goes to it, otherwise it goes to the front main speakers (you will notice that most systems will not permit you to select 'small' for the front stereo pair if you have the subwoofer set to 'off'). Some home theatre receivers permit you to choose the crossover frequency for bass management, but many use a standard value of 80 hertz.
Bass reflex link: A design for the enclosure of a loudspeaker. With bass reflex speakers the enclosure has a port that permits air to flow between the interior and exterior of the cabinet. The port is a hole, usually backed by a tube. The dimensions of the port are carefully calculated so that it permits bass at a selected frequency to be produced from the interior of the enclosure (driven by the back of the woofer's cone). This arrangement permits a bass reflex speaker to generally achieve greater efficiency than an acoustic suspension speaker, and it extends the depth at which bass may be produced without significant attenuation. However for frequencies below the band produced by the port, the output drops off quite rapidly.
Belt link: Sometimes the loop of material that is used to transmit rotational energy from motor to record platter on a turntable. Here, though, I am referring to a set of extreme audio system tweaks popularised in the 1980s and beyond by Peter Belt in the United Kingdom. These tweaks, for the most part, have no measurable effect on the sound produced by the system and there is no rational reason why they would affect, let alone improve, the sound of the system. They include such ideas as placing an extra sheet of paper in all books within the listening room, to ensure that there are an odd number of leaves in each book, placing a sheet of paper 'twixt the floor and just one leg of your listening chair and, more recently, freezing and then defrosting your CDs. Try not to laugh. Some subjective reviewers have, over the years, sworn by these measures.
Beta link: Or Betamax. The first widely-used consumer-level video recording system on the market. Developed by Sony in the late 1970s, it eventually lost out to the rival VHS system, which came to market about a year later, primarily because of shorter playing and recording times.
Bipole link: A loudspeaker designed to offer well-dispersed sound by firing its high frequencies, and in some models its full frequency range, in two opposing directions. Unlike dipole speakers, the sound is in phase from all the drivers.
Bit link: The smallest unit of digital information. A single bit can carry just one of two values: 0 or 1. There are eight bits in a byte, 1,024 bytes in a kilobyte, 1,024 kilobytes in a megabyte and 1,024 megabytes in a gigabyte. Sometimes, though, the traditional 1,000 is used rather than 1,024, leading to confusion. A bit should generally be abbreviated as lower-case 'b' (compared to 'B' for byte). Thus 128kb/s means 128 kilobits per second, whereas 128kB means 128 kilobytes.
Bit depth link: The size of the number that records each digital sample. Since the system is digital, the number relates to powers of two. The compact disc uses a bit depth of 16, which allows 65,536 different levels to be used to track the analogue source signal. DVDs usually also use 16, but may also use 20 bits (which gives over a million levels) or 24 bits (which gives more than 16.7 million levels). The greater the bit depth, the lower the harmonic distortion and quantization noise, and the more storage space required for the signal.
Bit rate link: The number of digital bits a system transfers per second. In general, the higher the bit rate, the higher the quality of the signal. In every case, the higher the bit rate, the more data space required. With audio bit rates are measured in the hundreds of kilobits per second (kb/s). With DVD video, they are measured in megabits per second (mb/s).
Bitstream link: The digital audio output of a DVD player, when switched to outputting the DVD's native digital audio format. Most DVD players can be switched to output a Dolby Digital bitstream, or convert the digital output to PCM.
Blu-ray link: A high capacity development of the DVD which uses higher frequency (blue) rather than red light frequencies for reading the disc. The combination of shorter wavelengths and other enhancements bumps up the maximum capacity from 8.5GB for a dual layer DVD to around 27GB, allowing the storage of high definition video.
Bob link: One of several strategies used in deinterlacing video. Bobbing is where each field is displayed all by itself in sequence. The intermediate lines are created by interpolating from the lines above and below it. This has the effect of reducing the vertical resolution at any instant of time by half (but it doesn't seem as bad as this, thanks to the interpolation), but smoothing pans because the two fields are displayed one fiftieth of a second apart. This is useful for video sourced material, in which the two interlaced fields constituting the full video frame were actually captured at slightly different times from each other, causing a combed effect on vertical lines. Compare weave.
Bonus group link: A Group on a DVD Audio to which access can be gained only through entering a four digit numeric password. Rarely, if ever, used for any actual content. See here for more.
Byte link: Eight bits. A byte can represent numbers between 0 and 255, or when interpreted as signed integers, between -128 and +127.
Cantilever link: The thin rod within a turntable's cartridge that transmits the movement of the stylus in response to a record's groove to the interior components of the cartridge that generate the electrical signal.
Carrier link: A sine wave which may be modulated by a signal to form an AM signal. The frequency of the carrier must be significantly higher than that of the modulating signal. In practice, the carrier is usually a radio frequency sine wave, and so is two orders of magnitude higher in frequency than the signal.
Cartridge link: The device that converts the movements of a stylus in the grooves of an LP to electrical signals. The cartridge is a small, light-weight device, secured to the end of a turntable's tonearm by means of two screws mounted 12.5mm apart. The movements of the stylus are transmitted through a cantilever to some form of electrical generating device. The two main types of cartridge are ceramic and magnetic. The latter is further subdivided into moving magnet and moving coil types.
CAV link: Constant Angular Velocity � as opposed to CLV. A method of spinning a disc or disk carrying a signal. CAV means that the rate of spin remains unchanged regardless of where the reading device is on the surface. An LP is an example (which is part of the reason why the outer tracks tend to sound better than the inner ones). While CDs are designed to be operated at a CLV, fast CD-ROM drives actually run them with a CAV.
CBR link: Constant bit rate � as opposed to variable bit rate. The signal (video or audio) is digitally encoded so that a fixed amount of data flows each second. This has the advantage of making the space requirements for the signal easy to calculate. DTS and Dolby Digital are both CBR systems, as are the earlier versions of MPEG audio and video compression. Most MP3 files are CBR encoded, although the format does support VBR as well.
CD link: Compact Disc -- This is the familiar 120mm optical disc. It carries a digital PCM representation of a two channel analogue signal, along with error correction information. The analogue signal is sampled at 44,100 hertz and uses a bit depth of 16.
CD emphasis link: When the compact disc was first developed, the designers implemented a rather surprising element in its specification. This was a pre-emphasis, de-emphasis cycle. In brief, this permits the treble in the source signal to be boosted before the CD is mastered (pre-emphasis), recording this fact by a special bit in the package around each segment of audio data, and cut again by the CD player (de-emphasis). When cut, it also had the advantage of reducing any noise due to the recording medium. But, in practice, there is no such noise, so initially it can be hard to see the purpose of this. Then when you consider that for most music the amplitude of the signal reduces as the frequency increases at around 6dB per octave, you can see that the amplitude of the higher frequency components would be very low and, consequently, subject to increased quantization noise. Boosting the higher frequencies significantly reduces this noise accordingly. The frequency response of the signal is pre-emphasised by boosting the signal from 50µs (microseconds -- which is what engineers used to specify frequency in some contexts) or 3,183 hertz, and levels out at 15µs, or 10,610 hertz, with a maximum boost of 10.45dB. CDs that actually use this are rather rare.
Ceramic cartridge link: A cartridge that produces an electrical signal through a piezoelectric effect. Such cartridges are rarely used in high fidelity applications because they require a relatively high tracking weight (usually upwards of 10 grams), have a low compliance and produce an uneven frequency response. However they do have the advantage of producing a rather higher output voltage than magnetic cartridges, and their frequency response characteristics approximate the RIAA equalization curve, allowing simpler circuitry to be used with the signal.
Chapter link: The divisions within a Title on a DVD Video. Navigation is most easily achieved by using the forward and reverse 'skip' keys of the DVD player's remote control.
Chroma link: The colour component of a TV picture signal. This comprises of two colour difference signals (the CR and CB) matrixed together. While these two signals are carried separately on a DVD, if the signal is delivered to the TV via an S-Video cable, they are matrixed together, slighty reducing colour clarity.
Cinch plug link: Another name, used by companies that presumably don't like to use the opposition's brand name in their own literature, for RCA plug.
Class A link: A power amplifier in which a sufficient DC bias voltage is applied to the power transistors so that the output signal always operates entirely in the positive or negative part of the cycle, entirely avoiding crossover distortion. This makes them quite wasteful of power since even at idle a considerable voltage is being generated. The DC bias is filtered out before being fed to the speakers.
Class A/B link: A power amplifier in which a certain amount of DC bias voltage is applied to the power transistors so that, at low power outputs, the output signal operates entirely in the positive or negative part of the cycle, avoiding crossover distortion. Thus, at low outputs, a Class A/B amplifier operates in Class A mode. At higher outputs the signal does cross over the zero point, effectively entering Class B territory. This design is a compromise between the efficiency of Class B amplifiers (in which there is no DC bias) and the elimination of crossover distortion in Class A designs. The DC bias is filtered out before being fed to the speakers.
Cliff effect link: Where the degradation of a signal's reception does not gradually increase with a reduction in signal quality or strength, but maintains full quality until some threshold, at which point the signal collapses into incoherence. Analogue transmissions tend to degrade gradually. Digital transmissions in modern systems (with error correction built in) tend to maintain full quality, but then cut out completely at the threshold.
Clipping link: When the amplitude of a signal reaches some limit determined by the equipment in use, it hits a ceiling (and floor) beyond which it cannot proceed. So the top and bottom of the wave is simply lopped off. The more it attempts to exceed the limit, the more that's chopped off, and the closer to a square wave the formerly rounded wave begins to look. This causes it to generate lots of harmonics, and so it sounds very distorted. The graphic to the right shows a sine wave at the left, and then the same sine wave amplified by just three decibels, to the right. This relatively minor clipping generates a third harmonic of 14%, a fifth harmonic of 3%, a seventh of 1.8% and so on. Truly awful sounding. Clipping is often caused by turning up an amplifier too loud so that its power limits are exceeded.
Clocking signal link: A signal used to synchronise items of equipment which are communicating digital audio or video signals to each other. The lack of a suitable clocking signal would allow their timing to drift apart from each other since their internal clocking signals would generally not be identical, so digital samples would be lost.
Cloth ears link: A purported characteristic of a person, the possession of which is alleged to account for his or her inability to notice differences in the sound quality produced by different pieces of equipment. Those so accused, assuming they have taken care to listen carefully to the demonstration, should forthrightly reject the allegation.
CLV link: Constant Linear Velocity � as opposed to CAV. A method of spinning a disc or disk carrying a signal. CLV means that the rate of spin varies in order to maintain a constant velocity of the track at the point where the reading device is on the surface. A CD playing back in an audio CD player is an example of this, because the CD player runs at about 500rpm at the start of the CD (where the inner grooves are being read), gradually reducing speed to about 200rpm as the track nears the outer edge.
Coaxial Digital link: The digital audio output signal of a DVD player in an electrical format, rather than optical. The data format accords with the S/PDIF specification.
Codec link: Compression/Decompression. A system which compresses a signal in some way for storage or transportation and then decompresses it at the point of delivery. Examples are MPEG, Dolby Digital and DTS. These systems use a codec to reduce the amount of data in the signal. Other forms of codec, particularly in the days of analogue audio systems, compressed and then decompressed the dynamic range of the signal, not to reduce the size of the signal but to reduce noise levels. One consumer system was called 'dbx'.
Colouration link: An unwanted alteration in the character of audio. Significant colouration of sound can make instruments and voices sound unrealistic. It may be caused by harmonic distortion, vibrations of component parts (for example, the panels of an inadequately braced loudspeaker enclosure) or, most commonly, through an uneven frequency response.
Colour difference link: These are two of the three components of a colour video signal. One is the Red colour difference signal, called variously Y-R or CR while the other is the Blue colour difference signal (Y-B or CB). They are created from the original RGB signal by creating a luminance signal (Y) and then subtracting this from the red and blue respectively (thus the name, colour 'difference'). When combined with the luminance signal the original three RGB signals can be recreated with very little degradation. The two colour difference signals and the luminance signal are, together, known as component video.
Compact cassette link: A neatly packaged magnetic tape recording and playback system for audio introduced in the 1960s. This uses a narrow plastic tape with four tracks running at a speed of 28.6mm/s (1 1/8 inches per second), contained in a sturdy plastic enclosure. In consumer equipment, only two of the tracks are accessible at any one time, providing stereo recording and playback. The tape is turned over (or an auto-reverse transport moves the recording and playback heads sideways) to access the other two tracks. Some semi-professional four track recording systems allow all four tracks to be recorded and played back at once, or even separately to permit multi-track recording. All cassette decks capable of recording (some are playback-only) have at least two heads: a record/playback head and an erase head. Some better decks include three heads, with separate record and playback heads to allow close-to real-time monitoring of the recorded material directly from the tape, and allowing the heads to be optimised for their different functions. While initially very low in fidelity, in the early 1970s tremendous advances were made in tape formulations, first with Chromium Dioxide magnetic materials and then later with 'Metal' tapes, which extended the high frequency response and improved their saturation characteristics. The addition of Dolby B noise reduction (and later Dolby C) reduced the inherent problem of high noise levels due to the low tape speed.
Compander link: Compressor/Expander. A noise-reduction system that works by compressing the dynamic range of the audio before recording, and expanding it again by an equivalent amount during playback. An example of this was the dbx system.
Compliance link: The degree of 'springiness' in a mechanical system. For example, the cone of a loudspeaker driver with a soft suspension which can move to and fro relatively easily is more compliant than one with a stiff suspension. The stylus of turntable cartridge with a high compliance tends to follow the excursions of the groove more easily than a that of a cartridge with low compliance.
Component video link: Three components of a video signal that, together, constitute the full signal. The three components are luminance (Y), red colour difference (CR) and blue colour difference (CB). These can be wrapped into each other to various degrees to form S-Video signals or composite video signals. On DVD the video signal is carried in component video form. The best way to deliver the DVD's picture to the TV is therefore via either component video connections (in which case, the TV reconstitutes the original RGB signal required for its CRT), or RGB (in this case, the DVD reconstitutes the RGB signal). For more on the quality differences between component video, S-Video and composite video, go here.
Composite video link: This is the way that the three component video signals are wrapped together to form a single signal, suitable for TV broadcast or carrying on a single two-conductor cable. The two colour difference signals are first matrixed together to form the chroma signal, and then the luminance signal is matrixed into this to create a single composite video signal. This process results in some cross interference between the chroma and luminance portions of the signal, reducing picture quality. For more on the quality differences between component video, S-Video and composite video, go here.
Compression link: Reduction. Air is compressed by squeezing it into a smaller space. Digital signals are compression by reducing the amount of data space required to hold them. Some digital data compresses readily, due to easily identifiable redundancy within the data. So, for example, a text document typically has a lot of space characters and 'e' characters, so other ways of expressing these can be found. Digital audio and video signal tend not to carry a lot of redundancy, so systems that compress these highly rely on eliminating some of the data and are consequently called lossy compression systems.
Compression driver link: A kind of loudspeaker driver. Rather than using a speaker cone to directly vibrate the air in a room, a compression driver has a throat in front of the moving part that causes a relatively small amount of air to compress and rarify rapidly in response to the movement of that part. This, in turn, drives the vibration of the air in front of it into the room, through some form of horn. Most compression drivers use piezo effects for the initial vibration, although some use more or less conventional cones. Compression drivers offer significantly higher efficiency than conventional drivers, allowing high output levels for a given input power, but can tend to reduce the dynamic range of the input signal and colour the sound.
Compression ratio link: The extent to which a signal (particularly digital signals) is compressed, expressed as a ratio of the uncompressed size to the compressed size of the data. MP3, for example, with a bit rate of 128kb/s has a compression ratio of about 11:1.
Contrast ratio link: The ratio between the darkest blacks (ie. the pixels in the area are fully shut off) and the brightest whites (pixels fully on) capable of being produced on-screen by a projector or other display device. For quality home entertainment work, this is a far more important than the ANSI lumens rating. LCD projectors typically have a specified contrast ratio of between 500:1 and 1,100:1. DLP projectors tend to start around 1,000:1 and the newer models can reach as high as 3,500:1. CRT projectors, noted for being the best at producing black blacks, are up around 15,000:1.
Constructive interference link: Where two signals, added together, act in sympathy with each other to boost the signal level. For example, bass from a subwoofer may, at certain frequencies, bounce from a nearby wall and that reflected signal may interfere with bass still coming directly from the subwoofer to effectively increase the output at that frequency. But it is also likely, at other frequencies, to result in destructive interference.
Crossover distortion link: A small discontinuity (or, at least, nonlinearity) in a signal when a transistor-based amplifier circuit switches from positive to negative operation. This is addressed by Class A and Class A/B designs. Sometimes called 'zero cross distortion'.
Crossover frequency link: The frequency at which a signal is handed from one component to another. This applies in crossover networks and bass management systems.
Crossover network link: The set of components in a loudspeaker that divides up the incoming signal, sending the bass to the woofer, the treble to the tweeter and, sometimes, the middle frequencies to a midrange driver. The crossover network uses resisters, capacitors and inductors (coils) to divide up the signal. Some high end systems use active crossover networks. In such cases, the division is made before the signal is amplified, so a separate amplifier is required for each driver.
Crosstalk link: Where a signal (particularly audio) leaks from one channel to another. Thus a voice may be intended to be entirely in the left channel of a stereo recording, but some portion of it appears in the right, dragging the apparent position of the voice somewhat towards the centre of the sound stage. Normally specified by the inverse of crosstalk: separation.
CRT link: Cathode Ray Tube: the guts of a traditional tube TV. Electron beams are fired from the narrow end at the back of the set towards the much bigger screen end. There they strike multi-coloured phosphor patches or stripes and emit the coloured light that you see. The appropriate signals are matched to the appropriate red, green and blue phosphors by means of either a shadow mask or an aperture grille.
Current link: The quantity of electrical charge moving through a circuit over a given time. The unit for current is amps or amperes.
DAC link: Digital to Analogue Converter. A component, circuit or device that converts a digital signal to an analogue one. Compare ADC which does the reverse.
Damping factor link: A specification for power amplifiers which suggests the degree of control that the amplifier exercises over a connected loudspeaker. It is the ratio of the nominal impedance of the speaker (and is typically quoted for eight ohms) to the internal impedance of the output stage of the amplifier. A high internal impedance for the amplifier means that its frequency response will vary with real-world speakers since their impedance varies across their frequency range. It also means that the driver, which wants to do its own thing under the influence of air, its suspension and so forth, rather than what the signal is telling it to do, will face a relatively high impedance to the voltage it is generating back into the amplifier. Consequently it will be freer to do its own thing, rather than what the amplifier is telling it to do. However the damping factor quoted for amplifiers does not take into account the impedance of the wiring between amplifier and loudspeakers, nor the impedance of the speakers' own voice coils. Consequently there is only a modest performance gain between a damping factor of, say, 60 and one of 600.
DAT link: Digital Audio Tape. A compact tape developed in the late 1980s by Sony which stores audio in PCM format. The tapes look very similar to the MiniDV tapes used in digital video cameras, but are somewhat larger, measuring 71mm wide by 53mm deep and 10mm thick. The reading part of the tape is protected by the casing. In order to pack sufficient capacity on, the tape is read using a helical scan head in the same way as a VCR. The default format for DAT is a 48 kHz sampling frequency and 16 bits of resolution, but they can also be switched to 44.1kHz.
dB link: Decibel. (See decibel.)
dBFS link: Decibel - Full Scale. The level of a signal, measured in decibels, with reference to the maximum possible level of the signal. With digital audio the maximum recording level is 0dBFS, so all measurements of the signal are negative values.
dBSPL link: Decibel - Sound Pressure Level. A measure of sound intensity. This is a logarithmic measure. To increase the sound level by three decibels, it is necessary to double the power output. A 10dB increase in sound level roughly equates with a perceived doubling of volume level. A figure of around 120-130dB is normally considered to be the threshold of pain. dB is sometimes loosely used as a synonym.
DC link: Direct Current. An electric current that retains its level and direction, at least in the short term. More generally, DC is also used to describe voltage sources that deliver this kind of current. DC is generally used at low voltages within electronic equipment. Batteries deliver DC. Compare with AC.
DCC link: Digital compact cassette. An attempted replacement for the compact cassette introduced by Philips in the late 1980s, early 1990s. This recorded audio in digital format, but used a lossy compression system. It failed to make headway since Sony's Minidisc had the advantage of direct access and, more recently, the recordable CD provides convenient and cheap recording with higher quality.
Deinterlace link: The conversion of an interlaced video signal to a progressive video signal. Two common systems are weaving and bobbing.
Decibel link: Abbreviation dB. A logarithmic measure of ratio. To determine the decibel relationship of, for example, two voltages you use the formula dB=20*log(V1/V2). If the result is negative, V1 is less than V2. If positive, then V1 is greater than V2. For power the formula is dB=10*log(P1/P2). dB is often used loosely as shorthand for dBSPL.
Destructive interference link: Where two signals, added together, act in opposition to each other and reduce the signal level. For example, bass from a subwoofer may, at certain frequencies, bounce from a nearby wall and that reflected signal may, if arriving back out of phase, interfere with bass still coming directly from the subwoofer to effectively reduce the output at that frequency. But it is also likely, at other frequencies, to result in constructive interference.
Dialog normalization link: In Australian, 'dialog normalisation'. Frequently called 'dialnorm'. A metadata indication in a Dolby Digital bitstream of the volume level of the dialog in an audio signal. Dolby Digital decoders can use this 'flag' to adjust the volume level of the whole audio stream, so that the dialog levels of different program sources remain the same. Most DVD movies have this flag set to '27', which means -27dBFS. If the decoder is set to act upon this, it will reduce the level of the signal by 4dB because it means that the dialog is set 4dB higher than the calibration level of -31dBFS. It is important to note that this volume adjustment is made not just to the dialog, but to the entire sound track. It is also important to note that it does nothing to the sound other than adjust the overall volume level. Whether or not the dialog normalization feature actually works as hoped -- in the sense of bringing the voice levels of all programs into line with each other -- depends entirely on the engineers who mix the sound setting the dialog to the appropriate level in the first place. Dolby Digital encoders typically default to the value of 27, and must be explicitly changed for a different value. Many home theatre receivers report dialog normalization with reference not to 0dBFS, but to -31dBFS (the calibration level), and so a level of -27dBFS is reported as -4dB.
Digital link: As opposed to analogue. It is a method of representing real-life signals (which are generally effectively infinitely variable) by using discrete numbers, usually binary numbers (a pattern of 1s and 0s). Holding discrete values, rather than the infinite number of intermediate levels used by analogue, makes digital signals relatively resistant to distortion and noise. The reason is that if any inaccuracy creeps in, unless very severe it will not affect the signal enough to throw it off. Consider a binary system. If all data is represented as either 0 volts or 1 volt, then it doesn't matter if some interference causes the 1 volt level to be sometimes 1.1 volts, sometimes 0.9 volts. The receiving module will regard any voltage as greater than 0.5 volts as 1 volt and treat it accordingly.
Digital audio link: Any one of a number of systems for recording sound using a digital representation of the sound. Some digital audio systems are straightforward representations of the analogue signal. Examples of these are PCM, DSD and MLP. Other systems take a simple digital signal (usually PCM) and process it heavily to reduce its size. Examples are Dolby Digital, MPEG audio and DTS.
D-ILA link: Direct Drive Digital Image Light Amplifier -- A projection technology used by JVC. It uses three reflective Liquid Crystal on Silicon panels which control light representing the signals for the three different colours.
DIN link: Deutsche Institut fuer Normung. A German standards body. DIN frequently appears in specifications to give an indication of how measurements were conducted, and also applies to a number of connectors approved by the body.
Dipole link: A loudspeaker designed to offer a diffuse, non-directional sound by firing its high frequencies in two directions, out of phase with each other, so that a listener receives few aural clues as to their exact location. To make such speakers work optimally, they should be placed so that the axis running through the front and rear tweeters is at 90 degrees to a line drawn from the speaker to listener. This will maximise the cancellation (see destructive interference) of direct radiation from the speaker to the listener's position.
Direct view link: A display device in which you look directly at the component which produces the picture. Thus a standard CRT TV is a direct view device, as is a plasma or LCD display. An RPTV and a front projection system are not direct view since you are looking at an image projected onto a screen.
Direct sound field link: A speaker system in which the great majority of the sound that you hear is coming directly from the loudspeakers, and very little from reflections from surfaces within the listening space. Direct sound field speakers tend to deliver a more accurate reflection of the source, and sharper stereo imaging, than reverberant sound field speakers. Direct sound field sound can be achieved by choosing speakers with restricted dispersion and placing them close to you.
Dispersion link: The degree to which loudspeakers spread their sound production in all directions, rather than directly to their front. All loudspeakers widely disperse their bass. But as the wavelength of a sound nears the size of a driver's cone diameter, the sound tends to become more directional.
Distortion link: An inaccuracy in the reproduction of a signal. In the case of audio, it is normally regarded as being composed of harmonic distortion and intermodulation distortion. But used more broadly, it can also encompass frequency response variations and noise. In the case of lossy compression technologies, some distortion consists of spurious noise (not harmonically related) surrounding the signal. When 'distortion' is quoted as a specification without qualification, it normally refers only to harmonic distortion.
Dither link: Very low level noise, usually 'white' in character, added to a digital audio signal to reduce harmonic distortion. It typically is just a random variation in the least significant bit of the digital signal. In some systems, such as Sony's SBM, the noise is shaped to yield a lower noise floor in the more easily audible midrange and low treble, by pushing much of the noise into the near-ultrasonic. Read more.
DLP link: Digital Light Processor -- a type of projector based on the DMD. Most DLP projectors use a single DMD, so to derive the three necessary colours they have a spinning wheel with colour filter windows, carefully synchronised with the signal driving the DMD. High end DLP projectors use three DMD panels, avoiding the need for the spinning wheels. This is likely to remove the Rainbow Effect that afflicts many DLP projectors. The main advantages of DLP projectors over LCD-based ones is that the narrower band of electronics around each active pixel on the DMD's surface reduces the screen door effect, and they produce significantly darker blacks (or, more correctly, they are better at stopping light from coming out the lens when a pixel is supposed to be black).
DMD link: Digital Micromirror Device -- a technology available (until the patents run out, it seems) only from Texas Instruments. This is used in DLP projectors and controls the transmission of light by means of hundreds of thousands of microscopic mirrors on its surface which physically swing through ten or twelve degrees in accordance with the signal. They come in a range of resolutions, from SVGA (800 by 600) through XGA (1,024 by 768) in the 4:3 aspect ratio, and 1,024 by 576 (woo hoo! A real PAL-optimised one!) to 1,280 by 720 in the latest Mustang HD2 DMD.
Dolby Digital link: Dolby Digital is an encoding scheme invented by Dolby Laboratories as a way of compressing digital audio so that it uses a lot less data space. It is also known as AC-3. Originally developed as an audio compression system for US digital television, it achieved prominence by allowing multiple channel sound tracks to fit onto standard 35mm cinema film prints (in between the sprocket holes on the film!), it has become the de facto standard for DVD. The compression system uses perceptual encoding, similar to DTS, MPEG audio (including MP3) and Sony's SDDS and ATRAC. It can carry up to 5.1 channels of sound, but does not necessarily have that many. Dolby Digital 2.0 (that is, stereo) can be encoded with Dolby Pro Logic surround sound. The Dolby Digital bitstream can also carry codes (metadata) to control playback parameters in the Dolby Digital decoder. Dolby Digital apparently supports bit rates of up to 640kb/s, but on 5.1 (or higher) channel DVDs the bit rates actually used at 384kb/s and 448kb/s. (Note, the 'k' here stands for 1,000, not 1,024). Dolby Digital bitstreams also include metadata for controlling the operation of the decoder.
Dolby Digital EX 6.1 link: A new surround sound standard which provides the usual 5.1 channels plus an additional channel: the centre rear channel. Unlike DTS ES 6.1 Discrete the additional channel is not carried discretely but is encoded into the two rear channels in a similar way to the front centre channel is encoded into a Dolby Pro Logic sound track. Movies prepared for Dolby EX 6.1 presentation in cinemas should have the same encoding on DVD. However EX 6.1 is compatible with 5.1 channel systems in the same way that Dolby Pro Logic is compatible with stereo systems. More correctly, this should be termed LucasFilm THX 6.1 since it was developed by them, but the name above seems to have come into common currency.
Dolby HX link: Dolby Headroom eXtensioin. Not to be confused with the various sorts of Dolby noise reduction, Dolby HX is a process that improves the high frequency, high level recording performance of magnetic tape, particularly compact cassettes. In order to provide reasonable performance linearity, magnetic tape needs to have a 'bias' signal applied to it during recording. This is an ultrasonic sine wave. Magnetic tape also has limits to the level at which it will record a signal. The problem is tape 'saturation'. You can only make the particles so magnetic, then they won't magnetise any further. Tape saturation tends to afflict higher frequencies more than mid and low frequencies. That is why many good quality cassette decks will maintain a flat frequency response all the way to 20,000 hertz at an indicated -20dB recording level, but roll off badly before that frequency at 0dB. Some proportion of a tape's signal-holding capacity is used by the bias signal. The Dolby HX system monitors the frequency and level content of the signal during the recording and when these reach certain levels, the system reduces the level of the bias signal, consequently allowing higher recording levels, particularly at high frequencies, to be reached before tape saturation. It relies on the signal to be self-biasing.
Dolby noise reduction link: It was the invention of an effective noise reduction circuit by Ray Dolby in the 1960s that got Dolby Laboratories onto the road to where it is today. This circuit was developed into Dolby Type A noise reduction, which became very widely used for professional analogue recording onto tape, prior to the advent of digital recording. Most analogue recording media produce background noise, typically like white noise. The simple solution would be to boost the middle and upper frequencies during recording, then cut them on playback, thus also cutting the hiss. But this causes overloading problems. Dolby noise reduction systems rely on the masking effect of sounds. If the signal was loud, the hiss would be largely inaudible anyway. So Dolby's system tracked the level of the signal, leaving it unaltered when it was strong, but introducing the boost/cut system when the signal was low. Dolby noise reduction later made it onto consumer equipment in the form of Dolby B, C and S noise reduction systems which all work along similar lines. It was Dolby B, in particular, that allowed the compact cassette to become an established media. Dolby HX, which also appears on recent cassette decks, is not to be confused with the noise reduction systems.
Dolby Pro Logic link: An improved version of Dolby Surround which decodes two channel Dolby Stereo sound tracks to four channels. In addition to the front left, front right and mono surround channels, it also extracts a front centre channel signal. The use of a centre channel improves the localisation of sound, particularly dialogue, for those viewers not seated directly in front of the screen.
Dolby Pro Logic II link: A further enhancement of the two-channel based Dolby Pro Logic, this cleverly decodes separate left and right surround channels from the original signal and eliminates the 100 to 7,000 hertz bandwidth limitations of the older system.
Dolby Stereo link: The original name for Dolby Surround, as it was used in cinemas. In cinema usage 'stereo' tended to mean some form of surround sound, although it was usurped by the home entertainment industry to mean two channels at the front of the room.
Dolby Surround link: The home equivalent of Dolby Stereo. This was the original system for decoding sound tracks for surround sound in the home, usually from video cassette. Dolby Surround sound tracks carry three channels of sound, matrixed into two channels. The Dolby Surround decoder extracts the additional channel, known as the surround channel, and sends it to a pair of rear or surround speakers. This surround channel is limited in frequency range to 100-7,000 hertz.
Driver link: The moving part, or parts, of a loudspeaker. These are usually woofers (bass drivers), tweeters and midrange drivers. There are a number of different driver designs. Virtually all woofers use the traditional speaker cone (some light material, often paper pulp or polypropylene) held in place by a suspension and backed by a coil inserted into the magnetic field of a strong permanent magnet. The amplifier's signal is fed into the coil, generating its own magnetic field, causing the coil and the attached cone to move. Midrange drivers, which are relatively rare these days, usually use either cones or domes (often polypropylene or a light metal such as magnesium), although there are some ribbon midrange drivers. Tweeters are most commonly domes (often polypropylene, silk or some other textile, or a light metal such as aluminium or titanium), but cheaper ones use cones. Some use inverted domes (that is, they are concave rather than convex), while some expensive speakers use ribbon tweeters. There was even, for a while, a 'plasma' tweeter where the high frequencies were generated by a pulsating ball of superheated air. Some speakers do not use what could be conventionally called drivers, for example electrostatic speakers.
DRC link: Dynamic Range Control. (See Dynamic Range Control.)
DRM link: Digital Rights Management. A catch-all name for various systems that control the distribution of digital audio and video content. Usually based on secure(-ish) keys and encryption.
DSD link: Direct Stream Digital. The digital audio format used in the SACD. Unlike the PCM system normally used, DSD uses a stream of single bits of information. The momentary level of the analogue wave form being represented by the bitstream is determined by the density with which the bits are 'on' rather than 'off'. It is modified by using noise shaping to increase the effective dynamic range in the main audible band. DSD uses for each channel a bit rate of 2,822,400 bits per second.
DSP link: Digital Signal Processor. A computer-type processing unit optimised to perform 24 or 32 bit floating-point operations on digital audio signals. This allows it to perform Fast Fourier Transforms and other complicated operations in real-time to apply frequency response adjustments, generate reverberation and even split-out certain frequency bands into separate channels. Many home theatre receivers incorporate DSP programs to generate ambient multichannel sound from stereo sources.
D-Terminal link: A video connection that delivers component video, along with useful ancilliary data. Despite the 'D', don't confuse it with any digital video standards such as DVI. The video signals are the same as component video (with up to 1080i high definition supported), while additional signals indicate the resolution of the video signal, whether it is progressive or interlaced, and its aspect ratio. The display device can use this information to set itself appropriately.
DTS link: Digital Theatre System. A high quality digital surround sound compression format capable of carrying multiple channels of audio. While using perceptual encoding like many other systems, it uses much lower levels of compression. DTS claims that it first uses non-lossy compression techniques to reduce or eliminate the need for perceptual encoding. Many users consider that it produces higher quality sound than Dolby Digital (see here for discussion of the validity of that view). DTS sound tracks come on DVD encoded at either 768kb/s or 1,536kb/s. (Note, the 'k' here stands for 1,000, not 1,024). The principle advantage of DTS over Dolby Digital is the implementation of DTS in the cinema. Rather than the digital data being optically recorded onto the film itself, DTS audio is recorded on a CD. Special CD players attached to the cinema's film projector keep the audio and film synchronised by means of time sync signals on the film. The advantage lays in the fact that in distributing foreign language sound tracks, only the CD needs to be different for each language, not the film.
DTS 96/24 link: A variation on DTS. However rather than using DTS's normal 20 bits of resolution and 48kHz sampling frequency (of the PCM data before it is encoded), it uses a 96kHz, 24 bit source signal, offering a theoretical frequency response to in excess of 40,000 hertz. DTS suggests that some of the higher resolution offered by this PCM standard carries through into improved audio quality. I have grave doubts about this. 96kHz, 24 bit PCM demands a 2,304kb/s bit rate for each channel. Since DTS 96/24 is offered as 5.1 channels, the equivalent PCM would need 11,520,000kb/s plus data for the subwoofer, yet DTS 96/24 is delivered with a compressed bit rate of 1,536kb/s, which means that a compression ratio of 7.5:1 has been employed. I would far rather all the available bits of data be employed in the most important (that is, audible) band of up to 20,000 hertz. (Note, the 'k' here stands for 1,000, not 1,024). DTS 96/24 DVDs are backwards compatible with standard DTS decoders.
DTS ES 6.1 Discrete link: A 6.1 channel version of DTS where a centre-rear channel is held in a discrete audio channel. DTS ES 6.1 DVDs are backwards compatible with standard DTS decoders.
DTS ES 6.1 Matrix link: A 6.1 channel version of DTS where a centre-rear channel is encoded into the two normal surround channels in a similar way to that employed by Dolby Pro Logic to hold a centre channel encoded into the two front channels. DTS ES 6.1 DVDs are backwards compatible with standard DTS decoders.
DTS Neo:6 link: A processing system that endeavours to extract an engaging 6.1 channel surround experience from two channels of audio. Unlike Dolby Pro Logic, this is not an encode/decode system, but more like a DSP system to generate something new.
Dual layer link: A type of DVD in which there are two physical data layers on the disc. The outermost one is semi-transparent, so a DVD player can focus its laser through this layer to extract data from the bottom layer. Such a disc has, in single-sided format, a capacity of 8.5GB, rather then the 4.7GB of a single layer DVD.
DV link: Digital Video. The format used to compress and record video on digital camcorders. This is based on Motion JPEG and is not the same as that used on DVD.
DVD link: Digital Versatile Disc or Digital Video Disc. In the former usage, it is the 12cm optical disc capable of holding masses of data for computer use, video, still pictures or audio. In the latter usage it is synonymous with DVD Video.
DVD Audio link: Digital Versatile Disc - Audio. This is the form of DVD which primarily holds DVD Audio material, all of which resides in a folder on the disc called 'AUDIO_TS'. The material may be either PCM or, more commonly, MLP encoded. The DVD Audio material can only be played on a DVD Audio player. DVD Audio discs almost always also hold a repeat of the material in DVD Video format so that they can be used in DVD Video players as well. Typically, though, the audio in this section is recorded in a lower standard of PCM, Dolby Digital or DTS.
DVD-R link: A write-once (ie. once recorded, it cannot be overwritten) recordable DVD. This format is supported by the DVD Forum. For compatibility issues, see here.
DVD+R link: A write-once (ie. once recorded, it cannot be overwritten) recordable DVD. This format is supported by the DVD+RW Alliance. For compatibility issues, see here.
DVD-RAM link: A rewritable (ie. recorded material can be erased or over-written) recordable DVD. This format is supported by the DVD Forum. It should noted that DVD-RAM has very limited compatibility with standard DVD players (although recent Panasonic models support it), because it uses significantly different technology to the other types of recordable DVDs. In particular, it offers true random access writing to identified sections of the disc, which has allowed Panasonic DVD recorders to implement a 'time-slip' feature (continuous recording, and the ability to rewind and watch recorded material, even while recording continues). It is also said to support a higher order of magnitude of re-write cycles than either DVD-RW or DVD+RW.
DVD +R DL link: A write-once (ie. once recorded, it cannot be overwritten) high-capacity recordable DVD. Unlike the competing formats, this version (announced 2003, product availability in 2004) is dual layer, allowing it to store up to 8.5GB of data rather than the 4.7GB of the other formats. This format is supported by the DVD+RW Alliance.
DVD recorder link: A consumer electronics device which uses one or more of several different types of recordable DVD media as storage for video and audio material. It acts as a replacement for the VCR, offering significant improvements in picture quality, plus the usual DVD playback conveniences of fast access, chapter breaks and the like. DVD recorders typically incorporate an analogue TV tuner for direct-from-broadcast recording, plus external inputs. One of the external inputs is often a DV port which accepts a digital signal from a digital video camera. However DVD recorders do not use the DV compression system for their video storage. They use MPEG2 the same as commercial DVDs for broad compatibility with DVD players. DV input is converted to MPEG2. They usually record sound using Dolby Digital 2.0, but some also offer PCM. There are two different kinds of media for making recordings which cannot be over-written: DVD-R and DVD+R. There are three different kinds of media which can be re-used: DVD-RW, DVD+RW and DVD-RAM. An increasing number of DVD recorders are multi-format, capable of recording to four different kinds of media. Most support only single layer recordable DVDs and thus offer a capacity of 4.7GB, however some are appearing with support for dual layer discs. DVD recorders permit different recording times, with longer times trading off for poorer quality. Very good quality recordings of two hours duration are achievable with a 4.7GB disc, while some offer six or more eight at low quality. Some premium DVD recorders incorporate a computer-style hard disk drive upon which recordings can be made, then edited, before being dubbed (at high speed) to a black disc.
DVD-RW link: A rewritable (ie. recorded material can be erased or over-written) recordable DVD. This format is supported by the DVD Forum. For compatibility issues, see here.
DVD+RW link: A rewritable (ie. recorded material can be erased or over-written) recordable DVD. This format is supported by the DVD+RW Alliance. For compatibility issues, see here.
DVD Video link: Digital Versatile Disc - Video. This is the form of DVD which primarily holds DVD Video material, movies or music videos. All the DVD Video material resides in a folder on the disc called 'VIDEO_TS'.
DVD-VR link: A recording mode offered for DVD-RW discs which differs from the standard DVD-Video mode. It allows significant levels of editing of recordings on the disc, at the cost of very limited compatibility with standard DVD players.
DVD+VR link: The recording mode provided for DVD+RW and DVD+R discs on consumer DVD recorders. While somewhat different to the standard DVD-Video mode used with commercial discs, it still provides for good compatibility with standard DVD players. On DVD+RW discs it allows significant levels of editing of recordings, while still retaining that good compatibility, and eliminating the need to 'finalise' the disc (DVD+R discs must still be finalised).
DVI link: Digital Visual Interface. A connection standard for delivering video in uncompressed digital format between signal sources (such as DVD players) and display devices. A rectangular 15-pin socket/plug is used for the connection. In home theatre contexts, DVD players and Digital Set Top TV Receivers with DVI outputs use the HDCP protocol to reduce the likelihood of digital copying. Read more here.
Dynamic power link: In some respects dynamic power is a similar measure to PMPO, but remains far more realistic. It is quoted in conjunction with continuous power outputs and shows how much power the amplifier or receiver can deliver for a very brief instant, such as when a crescendo is played in music. An amplifier with a reasonably low continuous power output can often sound quite good at reasonably high levels if it has a high dynamic power rating.
Dynamic range link: The differences in the volume level between the loud bits and the quiet bits of a movie or some music. On DVD these differences can be quite marked. This can lead to problems when trying to listen via your TV's speakers. The term is also used as a specification for DVD and CD players. In this sense it means the range between the loudest and the quietest sounds that the player is capable of producing, and is determined by the noise floor of the player and the medium.
Dynamic range control link: A facility in Dolby Digital to the reduce the dynamic range of the audio content in order to allow the entire program to be heard in adverse conditions. It does this by reducing the loudness of the parts of the program which are louder than the level set by the dialog normalization setting, and boosting those parts quieter than that setting. The parameters for reductions are carried in Dolby Digital metadata. This feature is useful for appreciating movies without disturbing neighbours, and when the audio from a DVD is being heard through a limited sound system. In particular, if DRC is available on a DVD player, it should always be switched on if a TV's speakers are being used to listen to the program.
Efficiency link: Used in connection with transformation of energy from one form to another, efficiency is the ratio of energy output to energy input in the transformation process. In regard to speakers, it is normally expressed as speaker sensitivity.
Electrostatic loudspeakers link: A form of loudspeaker in which the driver is a panel that responds to a varying electrostatic charge. Such speakers incorporate electronics which convert the moderate voltage, moderate current output from an amplifier into the high voltage, low current signal required to drive the panels. Electrostatic speakers are noted for producing little harmonic distortion and an excellent amount of detail in the reproduction of music. However they often present a difficult load upon amplifiers, can be subject to arcing (producing electrical sparks) in high humidity situations and tend to be somewhat inefficient. Because they use a large panel, these speakers do not employ an enclosure and so are bass limited. For this reason many models are hybrid, with standard woofers in an enclosure for bass. Electrostatic speakers are by their nature dipolar in operation since each side of the panel is generating an out-of-phase sound wave to the other.
Enclosure link: The box of a loudspeaker. In any half decent speaker, this is not merely a device to keep the drivers off the floor, but an integral part of the design of the whole loudspeaker, contributing greatly to -- or, if done badly, detracting from -- its performance. The most common enclosure designs are bass reflex and acoustic suspension. Good quality enclosures include strong bracing to resist sympathetic vibrations in their panels, which can lead to sound colouration.
Error correction link: Redundant data included with a signal in transmission or storage that allows the signal to be reconstructed even if some data has been damaged or lost. Error correction is used in most digital systems, from CDs through to digital television.
EQ link: Equalization (or, in Australian, Equalisation). An adjustment to the frequency response of some piece of equipment or process in order to achieve a desired outcome. It might be part of a standard process (eg. RIAA Equalization) designed to overcome physical limitations, or it might be used to correct unwanted frequency response inaccuracies imposed by a room.
Excursion link: The degree of fore and aft movement of a mechanical component in an audio system. Loudspeakers, for example, produce sound by vibrating their drivers' cones or domes. The distance between the furthest the cone, say, protrudes forwards and the furthest it moves back into the housing is the excursion of the driver. Woofers tend to have a greater excursion than drivers for higher frequencies. The drivers in some compact subwoofers deliver an excursion of up to 50mm. This wide excursion is necessary because output level is related to the area of the cone and the excursion. A smaller driver in a subwoofer can only provide equivalent output levels by allowing a greater excursion of the cone. Another example of excursion is the stylus of a cartridge. When playing a stereo LP it moves from side to side and up and down. Each of these is referred to as the excursion (horizontal and vertical) of the stylus.
FFT link: Fast Fourier Transform. A set of mathematical techniques for deriving an close approximation of the Fourier series for a real-world signal so that processing can be performed upon it. FFT is, with suitable hardware, sufficiently fast to allow real-time processing of signals. DSPs are based upon its mathematics (although, of course, they also do much processing work on the result of the FFT as well).
Fields link: The engineers who developed television had a problem: how to deliver massive amounts of video and audio over the air waves, yet have it able to be received and acted upon by affordable electronics. One of the many decisions they made was to halve the amount of data by adopting interlacing. This halved the bandwidth required for the signal. If the original picture source is a movie, it is displayed in the cinema at a rate of 24 frames per second. With PAL TV systems, the pictures are shown 50 times per second. What happens is that the movie is scanned into 576 horizontal line, but only every odd-numbered line is sent in the first 1/50th of a second. In the next 1/50th of a second, the even-numbered lines are sent. The TV shows first the odd lines, then the even lines (which are shown in between the fading remnants of the odd lines). The whole process of showing one frame takes 1/25th of a second (that is, a four per cent shorter time than the original movie's, so PAL movies have a slightly shorter run-time than when in seen in the cinema). Each half-picture shown in 1/50th of a second is called a field. Material sourced directly from video cameras is already broken up into fields before being recorded. The whole thing is far more complicated for NTSC TV. Consumer videotapes and DVDs conform to this scheme.
Firewire link: Apple Computer's name of a high capacity digital connection standard, capable of delivering up to 400mb/s. Frequently used for transferring video and audio from digital video cameras to DVD recorders and computers. Also known as IEEE1394 (the formal name) and i.link (Sony's name).
Fletcher Munson curves link: Experimentally derived results which plot the perceived loudness (by humans) of sounds across the audio spectrum. These suggest that our ears are very much more sensitive to midrange and low treble sound than they are to the bass and treble frequency extremes. The peak sensitivity occurs at around 4,000 hertz.
Flicker link: No, it's not the horse. It's the same phenomenon that gave the early cinema the nickname: 'the flicks'. It is the ability of the eye to see the dark interludes between each picture displayed on your TV, or at the cinema. Remember, a TV or cinema picture comprises of a series of picture frames shown in sequence, changing very rapidly. If the display flashes bright, but then fades away enough before the next frame is displayed, many people can perceive this as a slight flicker. It is more perceptible with unchanging flat colours on the screen, and with the peripheral vision. For TVs, it is more common for PAL than for NTSC because the former scans the whole screen 50 times a second while the latter scans at 60 times a second. This increase in speed reduces the ability to perceive flicker substantially. More expensive PAL TVs overcome this by doubling the scan speed to 100 times per second (displaying each frame twice). For another kind of flicker, that of horizontal lines flickering slightly up and down, see line flicker.
Flipper link: A DVD in which the movie is not entirely on one side of the DVD, so the DVD has to be turned over, or 'flipped', partway through viewing. Note, a DVD which has the movie on one side and some extras, such as a documentary or cast interviews, on the other is not a 'flipper' because the turning over doesn't interfere with enjoyment of the main feature.
Flutter link: A defect affecting analogue audio signal sources that rely on rotating the medium, particularly LPs and compact cassettes. Flutter is a rapid, repetitive speed variation, typically repeating at least ten times per second. If an LP or audio cassette undergoes this, it produces rapid variations in the playback frequency. At the slower end of the scale, it can sound like an unwanted tremolo or vibrato. At higher rates it can add an unpleasant harshness to the sound. Flutter is specified in per cent and specifications of more than around 0.1% are unacceptable. Digital sources such as CDs are immune to flutter because they lock their playback speed to a solid-state timing device.
FM link: Frequency Modulation. A system of storing or transporting a signal by using it to modulate a carrier in the frequency, rather than amplitude, domain. FM radio, high-fidelity audio on VHS, and numerous other systems are based on FM. FM tends to be more resistant to interference than AM.
Folder link: Formerly called a 'directory' under the DOS/Windows operating systems. This is a logical division on storage media containing files and other folders. It is relevant for DVDs because these use standard folders and files to hold their data. The folder holding the data for DVD Video is called VIDEO_TS while that for DVD Audio is called AUDIO_TS. Audio CDs, by contrast, do not use standard computer filing systems which is why their contents generally do not show up in a sensible form when inspected by standard computer file tools.
Fourier link: Actually, Fourier analysis. Fourier found that every repeating signal could be expressed as the sum of some particular sine wave, called the fundamental frequency, plus its harmonics at various levels. See, for example, square wave. This understanding permitted the development of all forms of signal processing, whether digital or analogue.
Four-way loudspeakers link: A loudspeaker which divides the incoming signal into four different frequency bands for distribution to drivers. It sends high frequencies to the tweeter, upper middle frequencies to a small midrange driver, lower middle frequencies to a larger midrange driver, and the lowest frequencies to one or more woofers.
Frames link: For movies, as seen in a cinema, this is an actual frame on the strip of film. Frames are shown in sequence, 24 times per second. On a TV or DVD, a frame consists of two fields which are interlaced together. For a PAL TV frames are shown at a rate of 25 per second (50 fields per second). For NTSC they are shown at 30 per second. If the original source of the picture is film, then the two fields constituting a frame in the PAL system consist of alternating lines from the same film frame, interlaced together. However if the material is video sourced, then the two fields will have been recorded 1/50 of a second apart. This can be seen on many DVD players by setting the still mode to Frame, rather than Field or Auto. Movies, when paused, while hold a stable picture. Video material (music clips, many TV shows and so on) will flicker, with moving objects appearing in two different places. Video material in the NTSC system appears in a similar way, but the transfer of film to NTSC uses a complicated 3:2 pulldown process.
Frequency link: The rate at which a repetitive signal repeats, measured in cycles per second or hertz (or its convenient multiples). Audio frequencies are generally in the range of 20 to 20,000 hertz because those are the frequencies to which the human ear sensibly responds. Equipment measurements often extend this range to 0 to 100,000 hertz. Video frequencies typically deal with a range of 0 to 7 MHz because that is the bandwidth available for PAL and NTSC signals. The human eye responds to light in the frequency range of 385,000 GHz to 789,000 GHz. The frequency of a signal can be calculated by dividing the speed with which the signal propagates through a medium by its wavelength.
Frequency response link: A measure of how accurately a system reproduces different frequencies. In the case of audio in a home theatre system, it is desirable for the frequency response of a whole system, including speakers and subwoofer, to be from 10 hertz to 20,000 hertz ±3dB. This performance requires a very expensive system indeed and, in practice, very few systems will produce bass down to anything like that bottom limit. Manufacturers who claim a frequency response for speakers of, say, 20 to 20,000 hertz without specifying decibel boundaries are telling you nothing. A tinny two inch transistor radio speaker can reproduce that range, although you won't actually hear it at either extreme because its output will be so low. Even subtle variations of less than half a decibel across the audio band can be quite audible, especially if they're spread over a fairly wide band of frequencies, and can thus change the character of the sound. Indeed, with speakers the single measure most closely related to their sound is the frequency response.
Fundamental frequency link: Any musical tone primarily consists of a particular simple tone (a sine wave) and a series of higher frequency tones, where the frequencies of those higher tones are whole multiples of the first-mentioned tone. The frequency of that simple tone is called the fundamental frequency. When we say that the Middle C of a piano has a frequency of 261 hertz, we are actually talking about its fundamental frequency, not that of the harmonics without which a piano note would have no distinguishing character.
GB link: Gigabyte. (See gigabyte).
Gigahertz link: A measure of frequency: 1,000,000,000 hertz.
GHz link: Gigahertz. (See gigahertz).
Gigabyte link: A measure of memory storage, a gigabyte equals (ie. 1,024 x 1,024 x 1,024 or 2³⁰) bytes, 1,048,576 (ie. 1,024 x 1,024 or 2²⁰) kilobytes or 1,024 megabytes. However, if used as a measure of hard disk storage, the 'giga' prefix normally means a round billion.
Group link: The major divisions for content on a DVD Audio disc. Typically the surround sound mix is in a different group to the stereo mix, while bonus video clips are in a separate group. This is the equivalent of a Title on a DVD Video. A Group is normally subdivided into Tracks.
Harmonic link: A tone the frequency of which is a whole multiple of another tone with which it is associated. Virtually all physical sound producers (including, unfortunately, loudspeakers) produce complex sounds which consist of a fundamental tone and many harmonics. Harmonics are also known (more in musical, than home entertainment, contexts) as overtones.
Harmonic distortion link: When a signal (usually audio) is not reproduced perfectly, it is said to be distorted. Harmonic distortion is a specific, and common, type of distortion in which a given frequency that is supposed to be in the signal has added to it overtones, or additional unwanted signals which are whole multiples of its original frequency (harmonics). Equipment suppliers often quote a measurement called THD or Total Harmonic Distortion. The lower the figure the better � in general. But relatively high levels of evenly numbered harmonics are easier to tolerate � indeed, can often be attractive, making the sound 'warmer' � than quite low levels of odd order harmonics.
Hass Effect link: Also known as the Precedence Effect. The human ears do not rely solely on different loudnesses to determine the direction from which a sound is coming; they also use timing. It is often the case that timing trumps loudness. If the same sound arrives from two different directions, the ear will tend to identify the direction of the source as that of the first sound to arrive, even if the other sound, arriving a few milliseconds later, is significantly louder. This is why it is important to properly adjust the time alignment of surround speaker systems. This effect is also made use of in high quality sound reinforcement systems in concert halls, since by delaying the sound coming from speakers near the back of the hall, it can be made to sound as though the high volume coming from those reinforcing speakers is actually coming from the front of the hall.
HDCD link: High Definition Compatible Digital. This is an encoding/decoding system intended to improve the resolution of CDs (and other digital audio sources) while retaining full CD compatibility. It is said to provide performance equivalent to a PCM system with a resolution of 20 bits, with retaining CD's bit depth of 16. The trick is in re-introducing the old-fashioned compander, albeit carefully implemented in a sophisticated digital fashion. This applies a 'limiter' to the peaks of the signal so that they can be reduced by 6dB, providing an effective two more bits of resolution. It also increases the level of low-level signals in the -45dBFS to -65dBFS range by up to 4dB, giving greater clearance from the noise floor. When played back with a HDCD decoder, the peak limiting and low level boost are reversed (a HDCD switching signal is embedded in the dither noise). HDCD also incorporates a dynamic low pass filter optimised for different types of signals (its operation is also signaled by the dither noise signal) and the dither itself is noise-shaped to provide a very low floor of noise and harmonic distortion below 16,000 hertz. I haven't analysed any HDCD CDs, but it seems likely that such severe noise shaping would produce a rather high noise floor between 16,000 hertz and the 22,050 hertz cutoff. Whatever benefits HDCD CDs may deliver when decoded with a HDCD decoder, it seems that the processing of the signal would adversely impact on playback in regular CD players. Read more at the HDCD site.
HDCP link: High-bandwidth Digital Content Protection. An encryption protocol developed by Intel and accepted for DVD use by the DVD Forum. This encrypts digital video output in real-time solely for the purpose of decrypting at the other end of a DVI or HDMI cable. It provides for two DVI-equipped devices to conduct a handshake, establish an encryption key, and then feed the video signal at full resolution in uncompressed digital format. HDCP supports high definition video signals as well. This system is supposed to protect against high quality digital video copying.
HDMI link: High-Definition Multimedia Interface. A new connection standard for feeding signals from sources to output devices in digital format. This carries both uncompressed digital video (in a form compatible with DVI) and uncompressed digital audio. Suitable encryption protocols are implemented on both (that for the video is HDCP) to resist digital copying. It has a huge bandwidth (up to 5 gigabits per second) allowing it to carry even 1080i video and, at the same time, up to eight channels of 24 bit, 192kHz digital audio. Plus it handles interaction between equipment, easing the way towards true single-remote-control of all devices. From a user perspective, though, it will mean that a DVD player need be connected to a home theatre receiver with just one cable (rather than the up to twelve currently: ana