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What is DVD Audio?

This version: 28 June 2003, previously published in DVD Now

Even before the CD was first introduced, some cliques in the audiophile world bemoaned the introduction of digital recording. Somehow, they claimed, digital sound reduces the ambience, the sense of being there, the sheer reality of a good LP pressing. Never mind the hiss in the grooves, the clicks and pops of the inevitable surface imperfections, the one percent distortion imposed when the master LP was cut -- the LP was better.

Over the years these diehards have gradually come to point the finger of blame for the CD's 'deficiencies' away from digital recording per se, and towards the digital standards adopted for the CD. Namely, CD's 16 bits of resolution and 44.1kHz sampling rate.

Two new formats are designed to address these issues, and to add a little something extra. These are Sony and Philips' Super Audio CD and everyone else's DVD Audio.

DVD Audio discs are physically identical to DVD Videos, with either one or two layers. Organisationally, though, they are very different. Both DVD-A and DVD-V are use computer style folders. The content of a DVD-V is held in a folder called 'VIDEO_TS'. It will not surprise you to learn that DVD-A content is in 'AUDIO_TS'. But a disc can be both, and indeed most DVD-A's are, with the DVD-A content backed with DVD-V content, usually recorded in Dolby Digital but sometimes in DTS. All the DVD-V content on such discs is in the 'VIDEO_TS' folder.

This Dolby Digital (or whatever) sound track is designed to allow you to buy a DVD-A today and play it on a standard DVD player, although the full benefits of DVD-A itself have await the acquisition of a DVD Audio player.

So what resides in that 'AUDIO_TS' folder? The primary DVD-A content is in a bunch of files called *.AOB. Like the *.VOB files for DVD Video, these are restricted to 1 gigabyte in size. With some discs, any bonus video content will be in *.VOB files but these are inaccessible to DVD Video players because they are in the 'AUDIO_TS' folder.

The selling point of DVD-A is the sound. It does not use DTS or Dolby Digital, but for the most part a new compressed format called Meridian Lossless Packing or MLP (sometimes called PPCM for Packed PCM). Packing in this context is another term for compression, but the compression is radically different to that employed by Dolby Digital or DTS. These use 'lossy' compression techniques which discard elements of the signal which are, on psycho-acoustic principles, thought to be inaudible. MLP preserves the entire linear PCM (pulse code modulation, the same system used for CDs) signal without tossing anything out, but manages to compress it down to around half of its original size. MLP also features radically improved data validation techniques to ensure that the signal, as delivered on the DVD-A, is identical to the master signal. Some DVD-As used standard PCM for the sound on some tracks.

The combination of moderate compression and the huge data space available on the DVD format means that recording resolutions higher than CD's 44.1/16 can be employed, and they are. And more than two channels can be delivered, and they are. The standards for DVD-A support from one to six channels, encoded from 44.1kHz/16 bits to 96kHz/24 bits. The most common sampling rates are 44.1kHz, 48kHz, 88.2kHz and 96kHz. In addition, DVD-A has a stereo mode supporting encoding up to 192kHz and 24 bits. This last one allows a bandwidth of around 90kHz.

DVD Audio players will not (with one exception) output the MLP signal digitally although some will output a 48kHz/16 bit version of the two main channels (which leads to interesting results from a six channel disc!) The exception is the DVD-A player from Meridian (which, after all, invented MLP) which encrypts the MLP bitstream so that it can only be decrypted by Meridian processors for delivery to Meridian digital speakers.

So for full use of a DVD-A player, you will require a receiver with six channel inputs. Since few if any receivers allow delay times or channel balances to be adjusted for the six channel inputs, the DVD-A player needs to have full-fledged configuration options in its setup. And here there is a problem. Of all the DVD Audio players I have tested so far (as at 28 June 2003), only one brand of DVD Audio players perform both bass management and speaker time alignment on DVD Audio discs. The brand is Denon and not all its models do this. But the three that do are the DVD-A1, the DVD-3800 and the DVD-2900.

Lack of bass management means that in most setups you won't get the deep bass properly reproduced. Lack of time alignment means that in most setups, the surround sound will be biased towards the back of the room (since the surround speakers are normally closer to the listening position than the front speakers). The sad result is that most DVD Audio players sound better playing the surround mix in (gasp!) Dolby Digital than they do in DVD Audio!

Before you hand over your money for a DVD Audio player, ask about these issues and get an undertaking to accept the unit back if it doesn't do these things properly.

© 2002 by Stephen Dawson