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Current Trends in the Recording Format Arena P2

by Dan Banquer August 30, 2004
Contributors:

SACD vs. DVD / DVD-A vs. CD

As the format war continues we need to take a close look at not only the proâs and cons but what this new marketing push is really all about.

Metric

SACD

DVD / DVD-A

CD

Sampling Rate

2.8224 MHz

(64 x 44.1 kHz)

Up to 192 kHz

44.1 kHz

Amount of Bits

1 bit

16 to 24 bits

16 bits

Dynamic Range

(Maximum)

104 to 108 dB

104 to 108 dB

96 to 98 dB

Copy Protection

Yes

Yes

No; at time of writing

Multi Channel Capability

Yes

Yes

Yes; but with very lossy compression

Brick Wall Digital Filter

No; analog filter

Yes

Yes

Video / Multimedia
Capability

No; audio only

Yes

Yes, but limited by storage capability


Sampling Rates: One of the major arguments against the CD is that the sampling rate is too low, and a higher sampling rate is needed to extend bandwidth and ease filter slopes.

There is evidence supporting this. How high is enough, however, is still hotly debated.

Amount of Bits: Adding more bits certainly gives more dynamic range and less distortion, but the best D/A converters can realistically only reproduce about 18 - 19 bits of resolution.

This is not about to change unless there is a major paradigm shift in the laws of physics.

Is 24 bits better than 20 bits? Not if all those other bits are lost in noise. SACD uses 1 bit at a very high sampling rate giving it an effective 120 db SNR in the audio band.

Copy Protection: At time of writing the CD has no copy protection, some have been adopted but withdrawn from the market due to major problems. New attempts appear to be made monthly. SACD and DVD-A both have copy protection schemes.

Filters for SACD and DVD-Audio

SACD Analog Filter:

SACD has no digital filter and relies totally on the analog low pass filter at the output of the DAC. This gives SACD a very distinct improvement in transient response vs. the standard CD. SACD also uses noise shaping and has a pretty high output of ultrasonic noise at approximately 100 kHz. Is this good for your tweeters? Sony says it's low enough to not do any damage.

The potential for abuse further down the line is a real possibility and a very questionable practice to many of us with extensive analog backgrounds. SACD uses an entirely different way of moving data through the digital domain, which Sony has called DSD. This was invented by Sony as an archival format because just about any of the present sampling rates used can be ãmovedä out of DSD and into a PCM format. Note:( The PCM format is the basis for CD and DVD-A.)

DVD-Audio Digital Brick Wall Filter:

DVD-A requires brick wall digital filters and very complex ones at that because they have to handle different sampling frequencies and different amount of bits. Brick wall digital filters are necessary to block any frequencies above¸ 1/2 the sample rate (aka. Nyquist Frequency) . This type of filter will cause transient response problems, but if the brick wall filter is placed far enough away the audio band, the problems lessen and audibility is no longer a major factor. In addition, digital filter manufacturers could also provide a transition slope on the higher sample rates to further lessen transient response issues. One recording studio that the author deals with did their own testing and found that practically every one heard the difference from 16 bits to 20 bits, and practically no one heard the difference when the sampling rate increased from 44.1 kHz to 96 kHz. The DVD-A specification requires 44.1 kHz, 48 kHz, 88.2khz, 96khz, 176.4 kHz, and 192 kHz.

It must also have capabilities to do 22.05 kHz, and 24 kHz for a separate subwoofer channel. The digital filter must also accommodate different word lengths, such as 16 bits, 20 bits, and 24 bits. This leads to very complex device that adds cost. It does not, however have much of any ultrasonic noise when combined with a properly designed analog low pass filter. The DVD-A specification allows the recording studio to use different word lengths, (amount of bits) and different sampling rates for each channel. For example: You can have the front four channels at 96 kHz, 20 bits with the rear channels at 48 kHz, 16 bits. You will not be assured that all of your channels have the full resolution that DVD-A is capable of, unless your liner notes say otherwise.

Video/Multimedia Capability :

SACD is an audio format only at present. At time of writing, we know of no other uses for the SACD format. SACD does offer a dual layer to include a CD track; DVD-A at time of writing does not incorporate the dual layer. DVD/DVD-A discs (blank discs) will be cheaper than SACD because of its broad range of users (Computers, audio, and video).

Despite what marketers and audio pundits claim, this format war is not about the battle for your stereo. CD's will be around for quite awhile. Is there a difference between a well-recorded CD vs. either SACD and DVD-A? Yes, but it's not the difference we heard 20 years ago when we compared LP's and Cassette tape to CD In the authors opinion, realistically it's about 5% better for stereo, which is not enough for many of us to start replacing our CD's with either one of these new formats. This format war is about the future of multi channel audio . CD's do not have the storage capability that SACD or DVD discs have. (650 megabytes for CD, 4.7 gigabytes for DVD-A and SACD)

While the newer audio formats such as DVD Audio and SACD do offer sonic improvements over Redbook CD, especially with their multi channel capabilities, one wonders if these new formats will suffer the same abuse or worse as current Redbook CD.

Initial Multi-Channel Releases
Both SACD and DVD-A have done initial releases of multi channel audio. Sales during the first half of 2002 are showing that the LP is still outselling multi channel SACD and DVD-A. It would appear that the public has some initial reservations about this. Note: According to the October issue of Sound and Vision: äStandard CDs still constitute over 94% of the market, cassettes about 5%, and vinyl LPs easily outselling both new high resolution format discs during the first half of this year 661,000 sold versus only 92,000!.

The bulk of present releases of SACD and DVD-A require six full frequency loudspeakers. (Derived from the DVD-A specifications) The individual channels are named, right front, left front, center, overhead, right rear, and left rear. When this type of system is set up correctly and we play back good recordings, the result is stunning to say the least. Not all of us, however, have the space and the money to do this. Many of us already have 5.1 systems that we use for home theater, and attempting to convert six full frequency channels to 5.1 is not without considerable problems as Gene DellaSala has outlined in earlier articles on this web site.

Bass management is a very real problem, so let us take another look at this for a moment.

If we attempt to apply bass management then we will need a unit that will allow variable filter slope, variable cut off, and variable phase to accommodate different types of speaker designs.

We will also need all of the bass information directed to the subwoofer. Then there's that pesky overhead channel. Do we mix that into the center channel? Or do we mix it into the right and left front channels? Having consumers attempt to adjust for all this is at best impractical and realistically improbable.

My guess is that if high-resolution multi channel audio is going to succeed there will have to be mixes for 5.1 systems. There are millions of 5.1 systems already in use in; why not take advantage of it? DTS has already successfully demonstrated this with multi channel DVD-A / CD music discs.

One final note: A new disc format is coming out of prototype that has 27 gigabytes of storage, and a blue laser to read it. If this new disc is released can we ask ourselves are DVD A and SACD obsolete, or will they be carried over to yet another media where people would have to buy new hardware to support?

We would like to thank all the people that are quoted here, for their suggestions, corrections, and permission.

Enjoy the Music!

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