| Media type | Optical disc |
|---|---|
| Encoding | Digital (DSD) |
| Capacity | up to 7.95 GiB/GB |
| Read mechanism | 650 nm laser |
| Developed by | Sony & Philips |
| Usage | Audio storage |
| Optical media types | |
|---|---|
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| Standards | |
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| See also | |
Super Audio CD (SACD) is a high-resolution, read-only optical disc for audio storage. Sony and Philips Electronics jointly developed the technology, and publicized it in 1999.[1] It is designated as the Scarlet Book standard. Sony and Philips previously collaborated to define the Compact Disc standard (as well as the S/PDIF digital audio cable specification). SACDs allow greater dynamic range and may hold more playing time than CDs.
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SACD is capable of encoding recorded audio in either stereophonic sound or surround sound. Although SACD audio streams are encoded in a pulse-density modulation (PDM) scheme called Direct Stream Digital (DSD), a manufacturer may also write a Pulse-code modulation (PCM) "layer" compatible with conventional Compact Disc players.
SACD is a disc of identical physical dimensions to a standard compact disc; the density of the disc is the same as a DVD and it encodes audio using a process known as Direct Stream Digital. The SACD sampling rate is 2.8224 MHz and the resolution is one bit. A stereo SACD recording can stream data at an uncompressed rate of 5.6 Mbit/s, four times the rate for Red Book CD stereo audio.[2] SACD recordings can have a wider frequency and dynamic range than conventional CDs.
| CD | SACD | |
|---|---|---|
| Format | 16 bit PCM | 1 bit DSD |
| Sampling frequency | 44.1 kHz | 2.8224 MHz[2] |
| Dynamic range | 96 dB | 120 dB[2] |
| Frequency range | 20 Hz – 20 kHz | 20 Hz – 50 kHz[2] |
| Disc capacity | 700 MB | 7.95 GB |
| Stereo | Yes | Yes |
| Discrete surround | Never implemented | Yes |
There are three types of SACDs:[2]
Almost all commercially released SACDs have included both stereo (dual-channel) and surround sound (multi-channel) mixes. A multi-channel mix need not be surround, however; some of the Living Stereo reissues (such as the RCA reissue of the 1957 Chicago Symphony Orchestra recording of Mussorgsky's Pictures at an Exhibition[4]) use only the three front channels to reproduce the original three-track (3.0) stereo recordings. Nor is a surround mix obliged to use all six SACD channels (five full-range plus LFE). For example, the 2001 SACD release of Mike Oldfield's Tubular Bells remains in the quadraphonic 4.0 mix.[5]
The CD layer exists primarily for backward compatibility, but is not required. If the CD layer is omitted, the SACD need not be limited to an 80-minute playing time. For stereo material, the space that would have been taken by the multi-channel program can be used to extend playing time to four hours or more. BIS has taken advantage of this to put all of Bach's organ music on five SACD-only disks.[6]
The Super Audio CD format was originally introduced in 1999.[1] Royal Philips Electronics and Crest Digital partnered in May 2002 to develop and install the first SACD hybrid disc production line in the USA, with a production capacity of 3 million discs per year.[7] But SACD did not achieve the same explosive growth that Compact Discs enjoyed in the 1980s,[8] and was not accepted by the mainstream market.[9][10][11] By 2008, some considered the Super Audio CD a complete failure.[12] However, the format continues to thrive in the audiophile community,[13][14] and new SACD recordings[15] and players[16][17] continue to be made.
Despite the global decline in Compact Disc sales, sales of Super Audio CDs and players increased in 2010.[18]
By October 2009, record companies had published more than 6,000 SACD releases, slightly more than half of which were European classical music. Jazz and popular music albums, mainly remastered previous releases, were the next two most numerous genres represented.[19][20]
Record companies issue most SACDs as backward-compatible hybrid discs. Such a disc can be played in high-resolution audio on a SACD player and conventional Red Book CD or DVD video players (albeit just with standard CD quality). The SACD format is thus backward compatible. SACD machines can play CDs and SACD discs; CD players can play SACD hybrid discs as audio CDs.[21]
Many popular artists have released some or all of their back catalog on SACD. Pink Floyd's album The Dark Side of the Moon sold over 800,000 copies by June 2004 in its SACD Surround Sound edition.[22] The Who's rock opera Tommy, and Roxy Music's Avalon, were released on SACD to take advantage of the format's multi-channel capability. All three albums were remixed in 5.1 surround, and released as hybrid SACDs with a stereo mix on the standard CD layer.
Some popular artists have released new recordings on SACD. Sales figures for Sting's Sacred Love album reached number one on SACD sales charts in four European countries in June 2004.[22]
As of May 2009, over 440 labels[23] have released one or more SACDs. Instead of depending on major label support, some orchestras and artists have released SACDs on their own. For instance, the Chicago Symphony Orchestra started the Chicago Resound label to provide full support for high-resolution SACD hybrid discs,[24] and the London Symphony Orchestra established their own 'LSO Live' label.[25]
Objective lenses in conventional CD players have a longer working distance, or focal length, than lenses designed for SACD players. This means that when a hybrid SACD is placed into a conventional CD player, the laser beam passes the high-resolution layer and is reflected by the conventional layer at the standard 1.2 mm distance, and the high-density layer is out of focus. When the disc is placed into an SACD player, the laser is reflected by the high-resolution layer (at 600 µm distance) before it can reach the conventional layer. Conversely, if a conventional CD is placed into an SACD player, the laser will read the disc as a CD since there is no high-resolution layer.[2][21]
Hybrid Super Audio CDs (which include both CD and Super Audio CD layers) can be played on CD players. The SACD layer can be played only on a player that supports the SACD format. Not all SACD players support multi-channel playback—some are simply stereo.
The Sony SCD-1 was a player which was introduced concurrently with the SACD format in 1999, at a price of approximately US$5,000.[26] It weighed over 26 kg (57 lb). The SCD-1, no longer produced, was introduced before multi-channel SACDs existed and played two channel SACDs and Red Book CDs only.
Many electronics manufacturers, including Denon,[16] Marantz,[27] Pioneer[17] and Yamaha[28] offer SACD players. None, however, has offered a portable SACD player capable of playing the high-definition layer of an SACD. Most portable CD players will play the conventional CD layer of a Hybrid SACD.
Sony has made in-car Super Audio CD players.[29]
Several brands have introduced (mostly high-end) Blu-ray Disc players that are SACD-compatible.[30]
SACD players are not permitted to offer an output carrying an unencrypted stream of Direct Stream Digital (DSD).[31] Players initially supported only analog output; later some proprietary digital interfaces such as Denon Link permitted encrypted transmission of DSD. There are now two standard digital connection methods capable of carrying DSD in encrypted form: i.Link and HDMI (version 1.2 or later, standardised in August 2005).
The older i.Link interface is generally found on older mid- to high-end equipment and some current top-of-the-line units from Japanese manufacturers. HDMI is more common, being the standard digital connection method for high-definition video with audio. Most new mid-level and higher 2007 model year and later A/V processors support the HDMI 1.2 specifications DSD over HDMI feature. Most boutique manufacturers still do not support DSD. Some HDMI 1.1 spec DVD players convert DSD to LPCM and then pass it to an HDMI 1.1 spec or later processor. Lower end processors usually convert the DSD to LPCM, higher end ones usually convert it to LPCM for bass management or DSP but can also process it natively at the expense of DSP and bass management. Some new DVD players from Oppo Digital, Pioneer, Onkyo, etc. now support HDMI 1.2 or 1.3 and will pass DSD over HDMI as well as LPCM. Be aware that some players, for instance, Onkyo DV-SP504, will not support DSD or LPCM over HDMI without resampling it to 48 kHz. SACD or DVD-A will be played through analog outputs instead. The older i.Link interface has been dropped from all but high-end A/V processors and DVD players.
The first two generations of Sony's PlayStation 3 (PS3) game console were capable of reading SACD discs. Starting with the third generation (introduced October 2007), SACD playback was removed altogether.[32]
For models that are capable of reading SACD, three output options exist:
PS3 was capable of converting surround DSD to lossy 1.5 Mbit/s DTS for playback over S/PDIF using the 2.00 system software. The subsequent revision removed the feature.[33] There is software available for creating a backup copy of a SACD using an older generation PlayStation 3.[34]
SACD audio is stored in a format called Direct Stream Digital (DSD), which differs from the conventional Pulse-code modulation (PCM) used by the compact disc or conventional computer audio systems.
DSD is 1-bit, has a sampling rate of 2.8224 MHz, and makes use of noise shaping quantization techniques in order to push 1-bit quantization noise up to inaudible ultrasonic frequencies. This gives the format a greater dynamic range and wider frequency response than the CD. The SACD format is capable of delivering a dynamic range of 120 dB from 20 Hz to 20 kHz and an extended frequency response up to 100 kHz, although most currently available players list an upper limit of 70–90 kHz,[35] and practical limits reduce this to 50 kHz.[2] Because of the nature of sigma-delta converters, one cannot make a direct technical comparison between DSD and PCM. DSD's frequency response can be as high as 100 kHz, but frequencies that high compete with high levels of ultrasonic quantization noise.[36] With appropriate low-pass filtering, a frequency response of 50 kHz can be achieved along with a dynamic range of 120 dB.[2] This is about the same resolution as PCM audio with a bit depth of 20 bits and a sampling frequency of 96 kHz.[2] Thus, DSD looks inferior to a "standard" PCM 24bit/96 kHz even using slightly more bandwidth than PCM (2.8224 Mbit/s vs 2.304 Mbit/s).
In the audiophile community, the sound from the SACD format is thought to be significantly better compared to older format Red Book CD recordings.[37] However, In September 2007, the Audio Engineering Society published the results of a year-long trial in which a range of subjects including professional recording engineers were asked to discern the difference between SACD and compact disc audio (44.1 kHz/16 bit) under double blind test conditions. Out of 554 trials, there were 276 correct answers, a 49.8% success rate corresponding almost exactly to the 50% that would have been expected by chance guessing alone.[38] The authors commented:
Now, it is very difficult to use negative results to prove the inaudibility of any given phenomenon or process. There is always the remote possibility that a different system or more finely attuned pair of ears would reveal a difference. But we have gathered enough data, using sufficiently varied and capable systems and listeners, to state that the burden of proof has now shifted. Further claims that careful 16/44.1 encoding audibly degrades high resolution signals must be supported by properly controlled double-blind tests.[39][40]
This conclusion is contentious among a large segment of audio engineers who work with high resolution material and many within the audiophile community.[41] Some have questioned the basic methodology and the equipment used in the AES study.[42]
Double-blind listening tests in 2004 between DSD and 24-bit, 176.4 kHz PCM recordings reported that among test subjects no significant differences could be heard.[43] DSD advocates and equipment manufacturers continue to assert an improvement in sound quality above PCM 24-bit 176.4 kHz.[44] Despite both formats' extended frequency responses, it has been shown people cannot distinguish audio with information above 21 kHz from audio without such high-frequency content.[45]
To reduce the space and bandwidth requirements of Direct Stream Digital (DSD), a lossless data compression method called Direct Stream Transfer (DST) is used. DST compression is compulsory for multi-channel regions and optional for stereo regions. This typically compresses by a factor of between two and three, allowing a disc to contain 80 minutes of both 2-channel and 5.1-channel sound.[46]
Direct Stream Transfer compression was also standardized as an amendment to MPEG-4 Audio standard (ISO/IEC 14496-3:2001/Amd 6:2005 - Lossless coding of oversampled audio) in 2005.[47][48] It contains the DSD and DST definitions as described in the Super Audio CD Specification.[49] The MPEG-4 DST provides lossless coding of oversampled audio signals. Target applications of DST is archiving and storage of 1-bit oversampled audio signals and SA-CD.[50][51][52] A reference implementation of MPEG-4 DST was published as ISO/IEC 14496-5:2001/Amd.10:2007 in 2007.[53][54]
SACD includes various copy protection measures of which the most prominent is Pit Signal Processing (PSP), a physical watermarking feature that contains a digital watermark modulated in the width of pits on the disc (data are stored in the pit length). 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 is legitimate. Because the majority of DVD players and all DVD-ROM drives use an optical pickup that lacks this specialized watermark detection circuitry, although they can read the data on the SACD layer, they cannot decode the audio of a protected SACD disc.[55]
On hybrid SACD discs, PSP is only applied to the SACD layer, not to the CD layer.
SACD has several copy protection features at the physical level which, for the moment, appear to make SACD discs difficult to copy without resorting to the analog hole, or ripping of the conventional 700MB layer on hybrid discs. These include physical pit modulation and 80-bit encryption of the audio data, with a key encoded on a special area of the disk that is only readable by a licensed SACD device. The HD layer of an SACD disc cannot be played back on computer CD/DVD drives, nor can SACDs be created except by the licensed disc replication facilities in Shizuoka and Salzburg.[56] But there is software available which allows ripping/copying a SACD using an early Sony PlayStation 3 Console.[34]
A number of new SACD players have encrypted IEEE 1394 (also called FireWire or i.Link) or HDMI digital outputs carrying DSD data, and it may be possible to get the raw DSD data from these links. The protection mechanism used is Digital Transmission Content Protection (DTCP), which can be used in "Copy Once" or "Copy Never" modes.
There seems to be one solution for obtaining digital non-DRM output on SACD as well as DVD-A players. A Switzerland based company is offering a modified output board that taps into the digital datastream prior to D/A conversion as well as converting DSD to PCM that the S/PDIF port can transfer.[57]
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