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Super Audio CD (SACD) is a high-resolution, read-only optical audio disc format developed by Sony and Philips Electronics, the same companies that created the Compact Disc. SACD is designed to provide high-resolution audio in both stereo and surround sound modes. SACDs use an audio format called DSD in addition to an optional CD-compatible layer using traditional PCM.

Introduced in 1999, SACD has not been accepted by the mainstream market, but new SACD recordings and SACD players continue to be made.

Overview

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 2822.4 kHz and the resolution is one bit. A stereo SACD recording can stream data at an uncompressed rate of 5.6 Mbps; four times the rate for Red Book CD stereo audio. 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 2822.4 kHz
Dynamic range 96 dB 120 dB
Frequency range 20 Hz – 20 kHz 20 Hz – 50 kHz
Disc capacity 700 MB 7.95 GB
Stereo Yes Yes
Discrete surround Never implemented Yes


There are three types of SACDs:
  • Hybrid: The most popular of the three types, hybrid discs include a Red Book layer compatible with most ordinary Compact Disc players, dubbed the "CD layer," and a 4.7 GB SACD layer, dubbed the "HD layer."
  • Single-layer: Physically a DVD-5 DVD, a single-layer SACD includes a 4.7 GB HD layer with no CD layer.
  • Dual-layer: Physically a DVD-9 DVD, a dual-layer SACD includes two HD layers totaling 8.5 GB, with no CD layer. It enables nearly twice as much data to be stored, but eliminates CD player compatibility. This type is rarely used.


Almost all commercially released SACDs have included both stereo and surround (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 ) 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 .

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.

Content

By October 2009, there were over 6000 SACD releases, slightly more than half of which were classical music. Jazz and popular music albums, mainly remastered previous releases, were the next two most numerous genres represented.

Today, most SACDs are issued as SACD 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.

Artist releases

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. 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.

As of May 2009, over 440 labels 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 , and the London Symphony Orchestra established their own 'LSO Live' label.

Disc reading

How a hybrid Super Audio CD works
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.

Playback hardware

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. 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, Marantz , Pioneer and Yamaha 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.

Several brands have introduced (mostly high-end) Blu-ray Disc players that are SACD-compatible.

SACD players are not permitted to offer an output carrying an unencrypted stream of Direct Stream Digital (DSD) . 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.

PlayStation 3 and SACD playback

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.

For models that are capable of reading SACD, three output options exists.
  • Using the AV output will give an analog stereo sound for SACDs that include a stereo track.
  • Using HDMI will give access to multi-channel high-resolution PCM audio (converted from DSD).
  • Using S/PDIF will give digital stereo sound (of either the stereo track, or a subset of the multi-channel mix)


PS3 was capable of converting surround DSD to lossy 1.5 Mbps DTS for playback over S/PDIF using the 2.00 system software. The subsequent revision removed the feature.

DSD

Technical background



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, and practical limits reduce this to 50 kHz.

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. With appropriate low-pass filtering, a frequency response of 50 kHz can be achieved along with a dynamic range of 120 dB. This is about the same resolution as PCM audio with a bit depth of 20 bits and a sampling frequency of 96 kHz .

Audible differences compared to PCM/CD

In the audiophile community, the sound from the SACD format is sometimes thought to be better compared to older format Red Book CD recordings. However, in controlled blind, level-matched listening tests over stereo reproduction subjects were not able to differentiate SACD recordings from their CD-quality converted version. Instead, the authors suggest that differences in particular mixes for the two formats may be causing perceived differences.:
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 highresolution signals must be supported by properly controlled double-blind tests.


Double-blind listening tests reported in 2004 between DSD and 24-bit, 176.4 kHz PCM recordings showed that no significant differences could be heard. Indeed, people have not been able distinguish DSD from CD-quality audio in blind listening tests; people cannot distinguish audio with information above 21 kHz from audio without such high-frequency content.

DST

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.

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. It contains the DSD and DST definitions as described in the Super Audio CD Specification. 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.A reference implementation of MPEG-4 DST was published as ISO/IEC 14496-5:2001/Amd.10:2007 in 2007.

Pit Signal Processing

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 they cannot read the data on the SACD layer of a protected SACD disc.

On hybrid SACD discs, PSP is only applied to the SACD layer, not to the CD layer.

Copy protection

SACD has several copy protection features at the physical level which, for the moment, appear to make SACD discs impossible 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 Shizuokamarker and Salzburgmarker.

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.

See also



References

  1. C|Net News, March 26, 2009 Betamax to Blu-ray: Sony format winners, losers by Steve Guttenberg. [1] "SACD was praised by audiophiles, but fizzled in the market. Sony Records no longer releases new SACD titles" (This is not entirely true; while Sony Classical does not appear to be making new SACD releases, Sony Classical in Germany and Japan made SACDs as recently as June 5, 2009 Sony Classical Germany Sony Music Japan) Retrieved on May 29, 2009.
  2. The Guardian, Thursday 2 August 2007 No taste for high-quality audio by Jack Schofield. [2] "Such a format—Super Audio CD (SACD)—has been out there since September 1999. And now, it's dying." Retrieved on May 29, 2009.
  3. Stereofile eNewsletter, January 10 2006. Io Saturnalia! by Wes Phillips. [3] Mentions "the failure of SACD and DVD-A to gain traction." Retrieved on May 28, 2009.
  4. Audio Video Revolution, October 19 2006. The Symbolism Of Losing Tower Records by Jerry Del Colliano. "The pure failure of SACD and DVD-Audio as high resolution formats was analogous burning down a small town." [4] Retrieved on May 28, 2009.
  5. Qualitron Imports Ltd. has SACD releases as recently as June 2009. Retrieved June 8, 2009
  6. Marbecks' SACD catalog also shows SACD releases as recently as June 2009. Retrieved June 8, 2009
  7. Extremetech.com, Leslie Shapiro, July 2, 2001. Surround Sound: The High-End: SACD and DVD-Audio. "A stereo SACD recording has a data rate of 5.6Mbps, which is four times the stereo CD data rate of 1.4Mbps." Retrieved on May 20, 2009.
  8. PC Magazine Encyclopedia Definition of Hybrid SACD Retrieved June 16, 2009
  9. ArkivMusic.com, Album Details: Mussorgsky: Pictures At An Exhibition, Etc / Reiner, Chicago "The three-channel remastering is equally successful" Retrieved June 3, 2009
  10. Amazon.com Tubular Bells Hybrid SACD "a pristine condition four-channel master of this legendary recording" Retrieved June 3, 2009
  11. BIS-SACD-1527/28 "20 hours+ of music on 5 SACDs for the price of 2! (Please note: These single layer stereo SACDs can only be played back on an SACD player)"
  12. High Fidelity Review. News. Retrieved on May 20, 2009.
  13. SA-CD.net
  14. High Fidelity Review. Universal Music Artists Hit SACD Gold and Silver in Europe. Retrieved on May 18, 2009.
  15. SA-CD.net. FAQ
  16. Chicago Resound label retrieved June 6, 2009
  17. London Symphony Orchestra—Buy Recordings retrieved June 6, 2009
  18. How A Hybrid Super Audio Compact Disc (SACD) Works "SACD players are equipped with optical pick-ups that emit a 650 nanometer wavelength laserlight that is reflected by the DSD layer. The optical pick-ups in all CD players, however, emit a 780 nanometer laserlight which is transparent to the DSD layer, so only the CD layer is read" Retrieved June 16, 2009
  19. Denon's web page shows a single SACD player, the DCD-SA1. Retrieved June 3, 2009
  20. Marantz's list of Hi-Fi Components shows one SACD player and Marantz's "Reference series" list shows four SACD players. Retrieved June 3, 2009
  21. The PD-D6-J and PD-D9-J are two SACD players that Pioneer offers. Retrieved June 3, 2009
  22. Yamaha's web page shows the CD-S1000 and CD-S2000] SACD players. Retrieved June 3, 2009
  23. practical-home-theater-guide.com SACD Playback Requirements and Content Protection "SACD compatible players are not permitted to send DSD digital content over an unencrypted digital audio link" Retrieved June 18, 2009
  24. Reefman, Derk; Nuijten, Peter. "Why Direct Stream Digital is the best choice as a digital audio format." (PDF) Audio Engineering Society Convention Paper 5396, May 2001.
  25. Ambisonic.net. Richard Elen, August 2001. Battle of the Discs. Retrieved on May 20, 2009.
  26. The Mariinsky Label FAQ, for example, claims that "The DSD process used for producing SACDs captures more of the nuances from a performance and reproduces them with a clarity and transparency not possible with CD." although there is no research backing up this claim. Retrieved June 9, 2009
  27. Meyer, E. Brad, and Moran, David R. Audibility of a CD-Standard A/D/A Loop Inserted into High-Resolution Audio Playback. Journal of the Audio Engineering Society (Engineering Reports).
  28. Blech, Dominikp; Yang, Min-Chi. "DVD-Audio versus SACD: Perceptual Discrimination of Digital Audio Coding Formats." (PDF) Audio Engineering Society Convention Paper 6086, May 2004.
  29. Toshiyuki Nishiguchi, Kimio Hamasaki, Masakazu Iwaki, and Akio Ando, "Perceptual Discrimination between Musical Sounds with and without Very High Frequency Components" [5] Published by NHK Laboratories in 2004
  30. practical-home-theater-guide.com Direct Stream Digital Technology Retrieved June 3, 2009
  31. dvdupgrades.ch


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