Setting the Record Straight on High-Resolution
Digital Audio
I was more than a little jarred recently when I read a
quasi-review of a new portable MP3 player in a highly respected newsmagazine. The article
was fine, except that the author claimed that the player produced better-than-CD-quality
sound. I then realized that the author, who is influencing an enormous audience, probably
didn’t know all that much about high-quality sound at all.
In terms of high-resolution digital audio for the home,
there are two new formats hoping to one day take over the position CD now occupies:
DVD-Audio and SACD. Both of these digital audio formats are capable of providing
better-than-CD-quality sound. MP3 simply cannot.
MP3 was never created to be a high-resolution digital audio
format. It was created to be easily transferred over low-bandwidth media such as the
Internet. In other words, the requirements were to have a file size that is extremely
small. And to that end, it is very successful.
MP3 makes files compact by using a lossy compression scheme
that actually discards certain data that is supposed to be relatively insignificant to the
human ear. The result is a very small-sized file that can sound surprisingly good,
particularly on low-resolution playback systems like computers, boomboxes, etc. Listen on
a higher-resolution home system, however, such as the ones we review here at GoodSound!,
and the musical deficiencies are more obvious. At best, MP3 can sound remarkably similar
to CD, but it can never sound better, simply because it throws away data resident on the
CD.
When CD was introduced to the marketplace in the early
‘80s it was not only touted as a convenient replacement for the LP, it boasted higher
resolution than the LP. To this day audiophiles still argue whether CD's 16-bit/44.1kHz
format is actually higher resolution, but it’s really a moot point now. In terms of
market share, CD occupies the top spot in terms of high-quality digital playback and will
likely continue to do so for a while. It’s the best we’ve got for the music
being released today.
CD revolutionized music storage for consumer audiences.
Instead of having sources that were analogous to the original analog music waveform
(i.e. LP, cassette, etc.), music was now being stored as digital bits -- supposedly
damage-proof and impenetrable to wear and tear. How they accomplished this was quite
impressive for the time. Essentially, to create the CD, each second of music was being
sliced in 44,100 discrete moments and each of those moments was assigned a digital number
16 bits in length. A CD player would simply read each digital word (i.e. the 16
bits) at a rate of 44,100 times per second, run it through a digital-to-analog converter
as it was doing so, and presto, the original waveform was back (in theory).
In theory, the combination of word length and sampling
frequency was ideal, and along with its convenient size and increased durability, CD was
sold as Perfect Sound Forever. Practice frequently diverges from theory, however,
and ever since the format’s advent it has long been criticized for still being too
low in resolution and for having a bit count and sampling frequency that weren't truly
capable of capturing complex musical information.
Digital experts predominantly agree that the number of bits
is not nearly as big an issue as the sampling frequency. Sixteen bits translates to 96dB
of dynamic range -- far more than LP and far more than we play back in our homes anyway.
However, studies on sampling frequencies (the 44,100 times the music gets
"sliced" per second) have shown that higher sampling frequencies than 44.1kHz
result in better sound quality. In fact, I talked to one leading designer who said that
his own company’s studies show that benefits can be obtained up to 500kHz! However,
he also cautioned that meaningful differences tapered off drastically about 192kHz.
Enter the world of DVD. Although one could use almost any
large storage medium to store higher-resolution digital (like a computer disk drive), it
wasn’t really practical until the advent of the Digital Versatile Disc. Compared to
CD it holds more than six times the amount of data on a single side. And now that this new
type of storage medium has successfully penetrated the market in terms of DVD-Video, audio
companies championing higher-resolution digital audio are using the technology and trying
to surpass the market penetration of CD.
On one side of the fence is DVD-Audio, or DVD-A for short.
This must not be confused with DVD-Video (although some newer DVD-Video players now
support DVD-A). This is an entirely different digital-encoding scheme compared to both CD
and DVD-Video. DVD-Audio boasts a word length of 24 bits (for a whopping 144dB of dynamic
range) and a sampling frequency up to 192kHz! In addition, the format is flexible enough
to be used with anywhere from two to six channels of sound. That means both stereo and
multichannel playback resolution are far greater than we have from CD or the film
soundtrack digital formats like Dolby Digital and DTS.
Then there is SACD, or Super Audio Compact Disc. Sony and
Philips, the original creators of CD, are championing this format and it’s not like
anything the consumer market has seen to date. The encoding scheme is based on Sony’s
proprietary Direct Stream Digital (DSD) format, which, they say, is far higher resolution
than CD and is much closer, in fact, to true analog than any other encoding scheme. Like
DVD-Audio, it can support two-channel and multichannel playback. And just like DVD-Audio
this is truly a higher-resolution format than CD, not like MP3.
Sounds exciting, doesn’t it? Unfortunately, mainstream
newsmagazines are not the only purveyors of bad information. The audiophile press has been
known to hand out a substantial amount of that from time to time. If you read some
publications in the late ‘90s you would have been thinking that by now either DVD-A
or SACD would have taken over CD. Nothing is further from the truth.
Today, CD is still the leader in terms of high-quality
digital audio, and for good reason. The format is very mature, quite inexpensive, and most
importantly, extremely good sounding. CD today is usually far better than it was in the
early ‘80s and through much of the ‘90s. Advancements in mastering,
digital-to-analog conversion, and various other things have resulted in a format that
satisfies the demands of the most discriminating audiophiles. Therefore, a good CD player
purchased today will be with you for many years to come.
Still, it’s important to know that there is better,
and in the case of high-resolution digital audio that means DVD-Audio and SACD. It most
certainly does not mean MP3. Which, if either, of these two true high-resolution formats
will dominate the market in the years to come is still up in the air. Just be aware
it’s coming and to keep abreast of the issue I recommend reading Jeff Fritz’s
monthly "Surrounded!"
column in SoundStage!. It focuses on precisely these issues.
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