| Video Noise December 2000
DVD-Audio: Peeking Behind the Curtain
OK, so you’re the guy who jumps on every new format in
the first or second year hoping to support the next best hope for higher-quality music or
movie sound. And you’re sitting there salivating over DVD-Audio. I mean how can you not
be impressed by resolution up to 24 bits and 192kHz! It just has to be audio nirvana
compared to CDs, even compared to 24/96 discs. 192kHz sample rates mean twice as much data
as is present in a 24/96 bitstream. DVD-A allows any number of channels from 1 to 5.1.
Cool lossless compression in the form of Meridian Lossless Packing allows you to get over
18Mbps worth of data into the just over 9Mbps DVD-Audio maximum data rate. DVD-A allows
assignment of different data rates to different channels so the most critical channels can
get the best quality signal. There are many cool things about DVD-Audio that make the
format seem irresistible.
Most people may assume that they just need to buy a DVD-A
player and plug it in and away they go. That’s true, sort of. If you aren’t
particularly interested in the best sound quality you can get from your system with DVD-A,
the old buy it and plug it in thing will work, no question. But if you’re looking
towards more fidelity, towards DVD-A being a leap forward in sound quality for either the
high-resolution 5.1 sound or ultra high resolution two-channel sound, there are some
things to think about before you jump on the DVD-A train.
The record companies and movie studios are piracy
paranoiacs. They are scared stiff about a system with the resolution of DVD-Audio being
crackable by pirates. The record companies have, so far, put the kibosh on allowing
DVD-Audio to escape any DVD-A player via any type of digital output. You are limited to
using 5.1 analog outputs for DVD-Audio. That’s a step back in time to about 1983 when
CD players did not have digital outputs. Almost every component anyone will connect a
DVD-Audio player to today operates in the digital domain. A/V receivers and surround
processors almost universally convert analog inputs to digital. So your DVD-Audio signal
path is going to look like this:
Digital disc >> Digital-to-Analog conversion in DVD-A
player >> 5.1 Analog connections to receiver or processor >> Analog inputs
converted to digital, often to 20-bit/ 48kHz digital, maybe to 24/96 if you have a really
new receiver or processor >> volume control and delay control >> converted
back to analog again >> to amplifier.
Even the newest AV receivers and processors touting 24/192
DACs will convert analog signals derived from 24/192 DVD-A back to 24/96 due to
limitations of the ADCs (Analog to Digital Converters). Furthermore, these same products
may flaunt their dual-differential DACs on 2, or even 6 channels. Yet the ADCs are not
dual differential. The 24/192 DACs may be the latest and greatest, but they will never
process a signal derived from an original DVD-A, 24/192 bitstream because of the
limitations of the analog to digital converters. The analog to digital conversion is most
often applied to inputs from cassette players, VCRs, TV tuners and the like where the
resolution of the ADCs is fine. But when the inputs are higher resolution formats like
DVD-A or even a phono cartridge, you really don’t want the additional conversion
steps if they can be avoided.
A few of the newest A/V Receivers and surround processors
have begun to include a set of analog direct inputs to save DVD-A inputs from the extra
digital to analog conversion that would normally take place. So if you are going to be
serious about DVD-A, you really need an A/V receiver or surround processor that includes a
set of 5.1 direct analog inputs so you can avoid two unnecessary conversion steps.
Lets talk about the analog output stages in DVD-A players
themselves. This is one very important area of performance when the DVD-A player is going
to do the processing and you won’t be able to use high-quality external DACs. When
high-end companies make disc players based on DVD players, they universally throw out the
DACs and analog output stage originally in the DVD player and replace them with something
more capable of producing high-end quality sound. I can pretty much guarantee early
adopters of the DVD-A format that the best sounding DVD-A players are going to be the ones
with the most high-end like analog output section, and perhaps the most comprehensive and
well-designed power supplies. Most DVD-A players are going to use similar chip sets and
similar DACs, so the main areas where they will differentiate themselves will be in power
supply technology and analog output stages. The more like a high-end preamp the analog
output stage is in the DVD-A player, the better the DVD-A player is going to sound. Most
DVD-A players will have op-amps in the analog output stage. Today that can be good news or
bad news. There are plenty of bad sounding op-amps; most of them are identified as
"audio op-amps." But there are some op-amps out there that sound just incredible
when they reproduce audio, but they are called "video op-amps" of all things
because they have the very high bandwidth capabilities needed to handle video signals.
Will the mainstream DVD-A manufacturers stick "video op-amps" in the analog
output stages of their players? I’d normally answer that with "not bloody
likely," but if you’d told me a year ago that there would be A/V receivers with
dual differential DACs, I’d have thought you were daft. So I won’t say it
isn’t going to happen!
The really hot setup for DVD-Audio would be an analog
6-channel preamp. However, this is a very rare breed! I only know of one 6-channel analog
preamp -- the R.E. Designs SCPA 1. Would you be able to get great DVD-A sound with the
R.E. Designs SCPA 1? It would be far better than the sound from a product that introduced
another analog to digital conversion, but you would still be limited by the sound quality
of the DVD-A player itself. If the DVD-A player is well designed, the SCPA 1 might just
reveal the best sound possible with DVD-A.
Where Will DVD-Audio Go In the Future?
For DVD-A to sound great, we are going to need a Firewire
digital interface to A/V Receivers or surround processors. Since a DVD-A Firewire
specification does not exist today, you can’t buy any hardware that might have
Firewire or a Firewire option and be assured that it will be compatible with a future
DVD-A implementation. The Firewire interface has a high enough bandwidth to allow all 5.1
channels of audio data, plus standard NTSC or PAL digital video data, plus ultra high
security audio and video copy protection. The music and movie industries will need the
protection to get cozy with digital outs from DVD-A players.
Of course there is no guarantee that this hypothetical
Firewire interface will ever happen. Nor is there any guarantee that completely
"transparent" copy protection for audio and video would be applied to this
problem. It is technically possible for the copy protection to be completely inaudible and
invisible, but will the industry be able to recognize either when they see or hear it?
Then there is the Firewire interface itself; it may have some problems that make it less
than ideal for audio and video data. Time will tell if this is true or not and whether it
is easy to overcome. Current Firewire implementations are for what I’d call
"non-critical" audio applications. Us audiophiles can get mighty picky when we
start to listen for problems.
If you want surround music, there is currently only one
serious contender to DVD-Audio, DTS Surround Audio Discs. They are compatible with the DVD
player you have today unless you have an early Generation 1 player that won’t pass
the DTS flag. DTS Surround music discs are compatible with most A/V receivers and surround
processors sold in the last 2 years or so and some of them sound pretty good with their
20-bit 48kHz bitstream spread across 5.1 channels. Use the digital output from your DVD
player into your A/V receiver or surround processor. No extra conversion steps involved.
There are a few Dolby Digital 5.1 music releases about, but the sound is distinctly
inferior to the higher data content DTS surround audio discs. Then there is the promised
full implementation of the SACD format that provides for a high-resolution SACD layer that
supports both high-resolution stereo and 5.1 surround versions of the album. The Red Book
CD layer would make these fully implemented SACDs backwards compatible with the CD player
in your car, in your bedroom, office or PC. DVD-A will need new players in all those
locations to be able to play the DVD-As you buy. The first full implementation of SACD
with multichannel sound has just appeared on the market so SACD is not out of the
"new audio format" contest yet. Of course, we'd like the full implementation of
SACD discs to cost a lot less than the $25 or higher list prices of stereo SACDs.
Hope this article has provoked some thought about DVD-A.
New formats always have their strengths and weaknesses and DVD-Audio is not exempt. If the
strengths outweigh the weaknesses or if the weaknesses are all quickly and summarily
banished, then DVD-A could be the next thing to amuse and delight millions of music
lovers.
...Doug Blackburn
db@hometheatersound.com |
