What
is SA-CD?
SA-CD
is short for Super Audio CD or, if you prefer, Super Audio Compact Disc
- an optical music carrier that may or may not be intended to succeed
the regular audio Compact Disc format introduced in 1983. In short it
is designed to provide better sound quality, both in the form of higher
fidelity and, optionally, in the form of multi-channel (surround)
sound, while maintaining backward compatibility with CD. For more
details, read on.
SA-CD was developed by Sony and Philips.
Who invented what exactly remains a secret shared between the two
companies but is quite irrelevant. The trademarks are owned by Sony.
Philips is the licensor of the disc format
and the trademark.
No, but we have run this FAQ against
some experts in these companies to weed out any factual errors and get
permission for using their illustrations.
That's to distinguish SA-CD from SACD,
la Société des Auteurs et Compositeurs
Dramatiques - a French copyrights body.
Scarlet Book is the name of the official
specification of the SA-CD format.
Traditionally the books containing the
format specifications of optical discs are named after a colour. A lot
of names had already been used: Red Book (Audio CD), Yellow Book
(CD-ROM), Orange Book (Recordable CD), Green Book (CD-interactive),
White Book (Video-CD),
Blue Book (Enhanced CD), even Rainbow Book (MiniDisc).
But there's more. Scarlet is not just red - it's a certain shade of
red. Sony and Philips might also have called it the Crimson Book or
Burgundy Book for all we know but it should be seen as a refinement of
the Red Book that defined the original audio CD, often referred to as
RBCD (for Red Book CD) or CD-DA for the official name 'Compact Disc
Digital Audio'.
A hybrid SA-CD is an SA-CD disc that can be
played on regular CD players. The sound quality in that case will, in
principle, not be better than that of a regular CD (though the
CD-compatible layer is usually derived from the high resolution signal
with SBM for better sound ... or similar words). The obvious benefit of
a hybrid disc is that you don't need to replace all your CD players by
SA-CD players at once. In fact you could even start collecting SA-CDs
before you own an SA-CD player.
Hybrid SA-CD works in a different way. Both
the CD layer and the high-density layer are 'read' from the same side.
The other side has a printed label, so it is easy to recognize the disc
and place it correctly in the tray of the CD player. How it works? The
high-density layer is partly reflective, partly transparent. At the
wavelength used by regular CD layers (780 nm) the SA-CD layer is
invisible so a CD player will just 'see' the CD layer. At the
wavelength used for DVD and SA-CD (650 nm), the SA-CD layer is
reflective.
In the early days of SA-CD,most titles were
released as 'single layer' i.e. SA-CD-only but nowadays virtually all
SA-CD releases are hybrid discs. Currently, more than 90% of the SA-CD
catalogue consists of hybrid discs and this rate continues to rise.
Yes. Single-layer SA-CDs look 'plain silver'
while hybrid ones have a goldish shine to them.
A hybrid SA-CD consists of a CD and
high-density layer while a Dual Layer SA-CD disc contains two
high-density layers, making it incompatible with CD players. The option
of a Dual Layer SA-CD, specified in the SA-CD standard, is intended to
provide more music capacity. Dual Layer SA-CDs are sometimes used for
special surround demo discs or for long classical
works.. They are relatively rare.
No, especially in the beginning many SA-CDs
released were stereo only. Nowadays most SA-CDs released are stereo
plus multichannel. Two thirds of all SA-CD titles are multichannel and
the general trend is up.
No. Unlike DVD-Audio, the SA-CD format does
not support 'down-mixing'. When an SA-CD contains stereo and
multichannel sound, these are stored
separately on the disc.
Nearly all of them do. There are a few
examples of hybrid SA-CDs that contain a multichannel mix but no stereo
mix in the SA-CD layer, even though the CD layer does contain a stereo
mix. Examples are the budget SA-CD series
by Universal's Eloquence label.
Not necessarily but in practice it generally
is. In some cases you may notice slight variations in playing time.
PSP is short for Pit Signal Processing - the
most prominent copy protection measure of the SA-CD format. PSP is a
physical watermarking feature that contains a digital watermark
modulated in the width of pits on the disc (whereas data is stored in
the length of the pits). The optical pickup must contain special
circuitry to read the PSP watermark, which is then compared to
information on the disc to make sure it's legitimate. Because DVD-ROM
drives use an optical pickup that lacks this specialized watermark
detection circuitry they cannot read the data on the high-density layer
of a protected SA-CD disc.
Pit Signal Processing has nothing to do with
PlayStation Portable, another PSP name coined by Sony.
DSD is short for Direct Stream Digital, the
way in which the analog sound signal is described in the digital
domain. It was originally invented by Sony for archiving studios'
master tapes with the idea that they shouldn't be left wondering ten
years later why they hadn't used a better encoding
scheme before transferring and discarding these masters.
Technical experts will tell you DSD is
basically a 1-bit Delta/Sigma conversion scheme. We'll try explaining
it in somewhat more understandable terms but cannot avoid using some
technical terms too.
Basically it works as follows: DSD being a
1-bit signal means that every bit represents a sample - a measurement
of the amplitude of the sound wave at a certain time. Since a bit can
only have two values, every bit in a DSD stream only tells weather the
amplitude of the sound signal was higher or lower than the previous
sample. Because it doesn't tell how much higher or lower the amplitude
is, you can imagine you need a lot of samples to accurately describe
the signal. Well, DSD uses 64 times the sampling frequency of CD: 2.822
MHz vs 44.1 kHz. The factor 64 is not randomly chosen. It's a power of
two, meaning that it's relatively straightforward to upsample from
typical
PCM frequencies including 44.1 kHz and multiples like 88.2 kHz.
PCM (Pulse Code Modulation) is a very
abstract way to describe an analog signal in a digital way but it's the
best way that existed at the beginning of the eighties when CD was
developed and introduced. In PCM, every sample consists of a
combination of bits (typically between 14 and 24, depending on the
carrier) describing the amplitude of the signal. The number of bits
determines the resolution of how finely the signal can be described,
where every added bit doubles the number of levels that can be
distinguished.
Converting from analog sound to PCM and back
to analog sound involves a fair number of processing steps, such as
quantization. Every step can cause further distortions such as
quantization noise, which has to be filtered out,
in turn again deteriorating the sound quality.
DSD on the other hand is an extremely simple
way of converting from analog to digital and back. The entire process
is extremely transparent. In fact, the DSD bit stream is so closely
related - perhaps analogous would be a proper term here - to the analog
signal that if you were to feed it to a speaker (as a series of +1 and
-1 values) you'd get back audible music.
Yes, it was and it did represent the state
of the art in 1982 - what could be put into a CD player but also what
could be put on a practical, 12-cm optical disc - but technology has
progressed and so has insight into human perception of sound. For
instance, it only became apparent later that although the human ear
cannot directly pick up frequencies above 20 kHz they are actually of
importance for the way we hear sounds. SA-CD with DSD extends the
frequency range towards 100 kHz.
A possibly more important difference between
CD's 44.1 kHz 16-bit PCM sound quality and SA-CD's 2.8 MHz 1-bit DSD
sound quality is the accuracy in the time domain. As it turns out, the
human ear is extremely sensitive to minute timing differences. In fact,
of the various cues our brain uses to determine the direction of sound
sources, probably the most important cue is the difference in time it
takes for a sound to reach our left ear versus the right ear. With a
sampling frequency of CD, 44,100 times per second it's very difficult
to reproduce a good 'sound stage' which is why you may find that the
sound of a CD often 'sticks to the speakers': you'll hear it coming
from the left speaker and from the right speaker but there's nothing in
between
- the proverbial 'hole in the middle'. This is an area in which DSD
excels.
Furthermore, at 120 dB the dynamic range of
SA-CD is much improved over CD.
Above all, SA-CD provides the option of
multichannel sound where Audio CD only offers stereo. More about that
later.
Although the audio on the high-density
layer of an SA-CD is always DSD or DST, the original recording may have
been made using (high-resolution) PCM technology, which is then
converted to DSD for the SA-CD master. Hence the confusing terms like
"24-bit 96 kHz SA-CD". The DSD sample rate was specifically chosen to
allow integer/fractional conversion from all PCM sample rates.
HDCD (officially an acronym for High-Density
Compatible Digital because the company that conceived this standard
could not use a name that included 'Compact Disc') is a variant of the
audio CD format that uses some otherwise unused 'subcode' bits to
enhance the resolution slightly. It's an elegant approach in the sense
that it provides the sort of two-way compatibility with CD like
described for hybrid SA-CDs above: HDCDs can be played on regular CD
players as if they were normal CDs: the player will simply ignore the
extra bits.
While it provides an improvement over 'Red
Book' CD it doesn't approach
the fidelity of SA-CD, or of DVD-Audio, for that matter.
HDCD was developed by a company called
Pacific Microsonics, later acquired by Microsoft.
Although both aim or aimed to succeed the
audio CD as preferred carrier for music by providing higher fidelity
sound and multichannel sound, there are a number of important
differences between the two formats.
- Compatibility - SA-CD provides the option of
compatibility with CD players by means of the hybrid disc (see What
is a hybrid SA-CD? above). While this is an option, in practice all
discs released nowadays are actually hybrid. Hybrid SA-CDs can also be
played on plain vanilla DVD-Video players but only in 'Red Book' CD
quality. DVD-Audio discs (other than Dual Discs) on the other hand are
not compatible with CD players. The format does however mandate added
tracks for compatibility with DVD-Video players. This can be in the
form of Dolby Digital, DTS or high-resolution stereo PCM.
- SA-CD
uses DSD audio format while DVD-Audio employs PCM. The difference
between DSD and PCM is explained above (see What is the difference
between PCM and DSD?). Many variations are allowed in DVD-Audio
content: sampling rates can be 48, 96 or 192 kHz; resolutions can be
16, 20 or 24 bits; the number of channels can go up to 5.1 - left,
right, center, left surround, right surround and LFE (Low Frequency
Effects). The creators of a DVD-Audio title however have to make a
trade-off between these parameters: 5.1 channels at 192 kHz sampling
rate with 24 bits resolution is not possible. A realistic combination
for multichannel sound, for instance, is 96 kHz for the front channels
and 48 kHz for the surround channels 24 bits resolution. For more
details about possible combinations refer here:
http://en.wikipedia.org/wiki/DVD-Audio#Audio_specifications
- On
SA-CD, the multichannel and stereo DSD mixes are stored separately on
the disc. The DVD-Audio standard allows the player to generate a stereo
downmix from the multichannel mix.
- SA-CD
supports up to six channels at full bandwidth. Rather surprisingly, in
its current form the SA-CD standard does not specify how the channels
shall be used precisely. Multichannel discs use 3 to 6 channels.
- The
SA-CD format permits additional data including text, graphics and
video. In practice however, only the text option is used. It works
similar to CD-Text in the Red Book CD format. While DVD-Audio is also
purely an audio format, the DVD format allows combination of DVD-Audio
and DVD-Video content on the same disc, even on the same side.
- The
catalogue of SA-CD spans over 4,500 titles with, on average, 70 new
releases added per month.
While the difference between regular audio
CD and the high-density layer of SA-CD can be quite easily perceived,
even to untrained ears, the sound difference between SA-CD/DSD on the
one hand and DVD-Audio/hi-res PCM on the other hand will be more
subtle.
A few dozen titles have been issued on both
formats so if you have a player that's compatible with both SA-CD and
DVD-Audio you can try for yourself.
Dolby Digital and DTS were developed for
movie sound effects and are perfectly tailored for that but less suited
for high-fidelity music reproduction. Both apply lossy compression
(much like MP3 does), whereas the DSD signal used on SA-CD does not. A
lossless compression scheme called Meridian Lossless Packing (MLP)
exists for DTS but this cannot be used with the DVD-Video format, only
with DVD-Audio.
Of course, on DVD it's possible to use
uncompressed PCM, even in high resolution up to 24 bit at 96 kHz, but
DVD-Video only supports stereo PCM.
Multichannel PCM is limited to the DVD-Audio format.
DTS-CD is a CD that contains 5.1-channel
audio in DTS format (bit rate: 1,378 kbit/s). It does not contain PCM.
It can be played on CD players with an 'SPDIF' digital output and on
DVD players, in combination with
an AV receiver that supports DTS decoding. See http://en.wikipedia.org/wiki/5.1_Music_Disc
DST is short for Direct Stream Transfer -
a losslessly compressed variant of DSD. Lossless compression means
every single bit from the original input stream is delivered at the
output after decompression, just like a zipped file on your PC would be
reproduced bit by bit, only DST is unzipped on
the fly. DST is used on multichannel SA-CDs .
DSD128 is DSD at twice the default
sampling rate: 5.6448 MHz. DSD128 is used in some studios for editing.
The normal DSD format is also called
DSD64 where confusion is possible.
DXD is short for Digital eXtreme
Definition - a sound encoding scheme for professional use that was
developed for editing high-resolution recordings because DSD is not
ideally suited for editing. DXD is a PCM-like signal with 24-bit
resolution sampled at 352.8 kHz - eight times 44.1 kHz. The
data rate is 11.2896 Mbit/s - four times that of DSD.
SBM is short for Super Bit Mapping - one
of various methods for down-converting an audio signal from a higher
resolution to a PCM signal with the desired resolution. It involves
techniques known as dithering and noise shaping. Direct SBM is the
method for converting a DSD signal to 16-bit 44.1 kHz PCM in one step
in order to minimize noise because every decimation step potentially
adds quantization noise. On hybrid SA-CDs with the Direct SBM label,
the audio on the CD-compatible layer is derived from the DSD master
using this process.
No, that isn’t likely to happen. Blu-ray
Disc (BD) and HD-DVD are
aimed quite squarely at storage of (high-definition) video and secondly
on data storage for computers. No audio-only variant of BD has been
specified, and as far as we know DSD hasn’t been included in the range
of optional audio formats on BD. You may consider SA-CD to be the HD
Audio complement to BD.
Both formats work with newer versions of
the multichannel audio
standards by Dolby and DTS: Dolby TrueHD and DTS-HD offering up to 7.1
channels of audio. Like Dolby Digital and DTS however, these audio
formats are primarily designed for use with movies.
A Super Jewel Box is a newer,
improved version of the ubiquitous original jewel case used with the
majority of CDs. You can recognize a Super Jewel Box by it's rounded
corners which are less prone to breaking when dropped, especially the
hinges. Another improvement is that it permits visuals on all six
sides, including the top and bottom surfaces. There are three versions:
a compact version, used with SA-CDs, a medium-sized version, used with
DVD-Audio discs and a tall version used with some DVD-Video discs,
mostly
music titles.
No, some SA-CDs are packaged in
traditional jewel cases, digipacks or other forms.
No, a Super Jewel Box is certainly
no guarantee for an SA-CD, especially since Universal Music has started
using them for many most of their new
releases in 2006.
Hybrid SA-CDs you can play on every CD
player. Only single-layer SA-CDs cannot be played on regular CD
players.
Of course if you have a regular car CD
player you can play the CD-compatible layer of hybrid SA-CDs. If you
want to enjoy them properly however you'll need a car SA-CD player.
Since Q1 2007, Sony has a range of such players for the 'aftermarket',
including stereo as well as multichannel models.
As of the same quarter, Bose has
announced a 'universal media player' for cars, supporting SA-CD as well
as DVD-Audio. This, on the other hand, is a line-fit model, i.e.
factory-installed. Thus far it's only available
in one Ferrari model.
Most DVD players simply recognize (and
play) an SA-CD as a CD. A few early models can be confused because
before they spot the CD layer they
detect a DVD layer with content that they can't decode.
So far no HD-DVD player with SA-CD
support has been announced and the only SA-CD-compatible Blu-ray Disc
player is Sony's PlayStation 3.
Hybrid SA-CDs can be played as CDs on
all consoles that support ‘Red Book’ audio CD. The high-density layer
will only play on a PlayStation 3. The output is just stereo via the
analog AV out. The SPDIF output is silent during SA-CD playback.
Multichannel audio is available only via HDMI however the signal is not
DSD but high-resolution PCM: 24-bit at 176.4, 88.2 or 44.1 kHz
(configurable as of firmware version 1.90).
The SA-CD layer cannot be played in
any PC drive - not even in those Sony VAIO PCs that support DSD audio.
The CD-compatible layer of hybrid SA-CDs can be played but some early
CD/DVD drives have difficulties due to misdetection (mistaking the
high-density layer for a DVD). Pure CD-ROM
and CD-R/RW drives that do not support DVD will work reliably.
According to estimates by Sony,by
June 2007 "the cumulative quantity of SA-CD hardware delivered to
market is around 20 million including PlayStation 3. The number of
models available in the market would be now close to 200
from 43 manufactures". We know of no information that contradicts this.
Of course, for a multichannel
speaker configuration you'll need more speakers and cables than for a
stereo setup. Regarding quality, the same counts as for the amplifier:
even with mainstream speakers and cables you'll be able to appreciate
the sound quality improvement of SA-CD over CD, because the wires will
typically not be the bottleneck. Once you have upgraded other parts of
your chain (the player, the music carriers) you may however become more
critical of your speakers and cables, and there is no limit
as to how far you can go.
Many home theater systems are
primarily designed for use with Dolby Digital and DTS where having
relatively small surround speakers and larger is perfectly normal,
often supported by a setting on the receiver to switch between
identical speakers and larger plus smaller speakers. Multichannel SA-CD
is best enjoyed with five identical speakers (plus an optional
subwoofer; see the next question) or at least with rears from the same
speaker family but that doesn't mean you won't be able to enjoy great
sound until you've
upgraded all of your speakers.
This depends on your taste as well
as your receiver. Note that even multichannel titles often do not use
the .1 channel. If you're not using a subwoofer it's helpful if your
receiver has a feature called 'bass redirection', to make sure you
don't miss too much. Some SA-CDs include a duplicate of the bass signal
on the .1 channel for use with sub-sat systems which will
need to attenuated or disabled on full range systems.
Great one!