Klarinet Archive - Posting 000026.txt from 2003/09

From: "Benjamin Maas" <benmaas@-----.com>
Subj: RE: [kl] Hybrid CD (long, technical answer)
Date: Tue, 2 Sep 2003 22:35:51 -0400

> -----Original Message-----
> From: Gil Guerrero [mailto:gilster@-----.com]=20
>=20
>=20
> I believe that this indicates that it is a Super Audio Compact Disc,=20
> that also has the conventional compact disc-compatible audio on it as=20
> well.
>=20
> SACD is the new high quality format that is being put forth by=20
> several manufacturers, so that I will be forced to buy all of the=20
> works of Thelonious Monk again. Eventually these discs will have=20
> mutiple channel data, similar to DVD audio.
>=20
> There is an ongoing debate as to whether it is better than DVD.
>=20
> Hope this helps.
>
=20
Almost got it right, but not quite. Hybrid does usually (but not =
always)
refer to a dual-layer CD with a SACD and a regular (red book) CD layer.

SACD does indeed stand for Super Audio CD. There is a format war going =
on
between 2 new formats of high-resolution, multi-channel "CDs." The two
formats are SACD and DVD-Audio. Don't confuse DVD-Audio with DVD-Video =
that
most of you probably own already...

"Regular" (Red Book) CDs are digital music delivered in the 16 Bit 44.1
Kilohertz PCM (Pulse Code Modulation) format. In terms that you can
understand. If you imagine the waveform split into 44,100 samples every
second. Each of those samples is mapped as to its dynamic over 16 bits
(2^16 levels of music). According to Nyquist, that enables a top =
frequency
of 22,499Hz to be represented. (~1/2 the sample rate). Because most
people's hearing tops out at 14-16 KHz, that was deemed to be plenty of
resolution for listening. The other limit of CDs is that they are =
stereo (2
channels) only.

About 5-7 years ago, people started noticing that there was a particular
"sound" to digital recording that they felt was not complimentary to the
music. Was they started to realize (through psycho-acoustic =
experiments) is
that while the body cannot hear above roughly 16KHz, it was aware of
harmonics that reach far above that. The problem is that because of the
Nyquist law, those frequencies could not be replicated using was was the
conventional recording technology. Also, people started experimenting =
by
increasing the bit depth at which recordings were made. The immediate
effect of that is that the noise floor (noise level) of the recording =
went
down. This was especially apparent when summing/mixing multiple tracks
together.

The first experimentation was with increasing the sampling rate of the
recordings to be able to reproduce those higher frequencies. A sampling
rate of 96,000 samples per second allows for reproduction of 47,999 Hz. =
It
has been noted that this does a lot to affect the sound of the =
recordings...
Now, recordings are being made with sampling rates of 384KHz and higher. =
I
won't get into the discussion as to how much of a difference this makes.
Obviously since people are recording at such high sample rates, a format =
had
to be created to handle this. DVD was the quick answer. By this point =
DVD
Video had become the single most successful consumer technology roll-out =
in
history. To adjust this format for the new music recordings made a lot =
of
sense. Thus DVD-Audio was born. Eventually, when the arguments about
format settled, it is not only high-definition, but also multi-channel =
(for
surround sound recordings).

About 4 years ago or so, Sony (and Phillips, too) decided to splinter =
off of
the DVD-Audio bandwagon and develop their own format. It worked with =
CDs so
why not? They developed a whole new technology called DSD (Direct =
Stream
Digital) for release on a new CD format called SACD. This is a =
completely
different method of digitizing music and therefore has its own set of
problems. First of all, the way it works is that the music is digitized =
at
an extremely high sampling rate, but at only 1 bit of resolution. If =
you
can imagine a sampling rate of something like 3.8 Megahertz (million =
samples
per second) where the sample being made is in relation to the sample =
before
it (higher or lower). This is DSD. From a technological standpoint, it =
is
very difficult to work with because every edit and calculation affects =
the
entire rest of the recording. By now, there are some, but not many, =
tools
to deal with this- They are very expensive, though (many 10's of =
thousands
of dollars). To help make SACD competitive with DVD-Audio, they =
eventually
expanded the format for a mutli-channel (surround) format as well. Some
SACD Hybrid Discs are SACD only with the Hybrid referring to both a
2-channel as well as a 5.1 channel mix.

Which will win? Most engineers I know believe that DSD sounds better =
than
PCM. Many (like myself) don't care because our clients listen on $200
stereo systems and think that MP3s sound good. Personally, I record
everything at a high-bit rate (24 bits) as that makes a pretty huge
difference in the sound. I don't usually do 96K or higher recordings
because it is tough for me to hear a difference (and I've got a *VERY* =
high
quality listening system).

Both formats will probably fail because radio and people's car stereos =
are 2
channel only (sometimes only mono!) and those of us with 600+ CDs in our
collections aren't going to purchase them all again in a new format... =
Both
formats DO sound considerably better than regular CDs (as opposed to =
MP3s
which sound considerably worse), but neither will probably do well in =
the
consumer marketplace. For examples, look at Beta video and DAT tapes.

--Ben

Benjamin Maas
Fifth Circle Audio
Los Angeles, CA
http://www.fifthcircle.com

---------------------------------------------------------------------
Klarinet is supported by Woodwind.Org, http://www.woodwind.org/