Super Audio CD

Super Audio CD

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

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. Introduced in 1999, SACD has not been accepted by the mainstream market,^[1][2][3][4] but new SACD recordings^[5][6] and SACD players^[7][8] continue to be made.

Contents 1 Overview 2 Content 2.1 Artist releases 3 Disc reading 4 Playback hardware 4.1 PlayStation 3 and SACD playback 5 DSD 6 DST 7 Pit Signal Processing 8 Sound quality of SACD vs CD 9 Copy protection 10 See also 11 References 12 Bibliography 13 External links

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 the 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 higher than the rate for Red Book CD stereo audio.^[9] SACD recordings can have a higher frequency response and dynamic range than conventional CDs.

	CD	SACD
Format	16 bit PCM	1 bit DSD
Sampling frequency	44.1 kHz	2822.4 kHz[9]
Dynamic range	96 dB	120 dB[9]
Frequency range	20 Hz - 20 kHz	20 Hz - 50 kHz[9]
Disc capacity	700 MB	7.95 GB
Stereo	Yes	Yes
Discrete surround	Never implemented	Yes

There are three types of SACDs^[9]:

• Hybrid: The most popular of the three types, hybrid discs include a Red Book layer compatible with most legacy Compact Disc players, dubbed the "CD layer," and a 4.7 GB SACD layer, dubbed the "HD layer." ^[10]
• 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.

SACDs are usually authored with a two-channel DSD mix, but this is not mandatory. They may contain a discrete surround sound mix with up to six channels. Although the disc always stores all channels, the surround mix does not have to use them all, and some may be mute; for example the 2001 SACD release of Mike Oldfield's Tubular Bells remains in the quadraphonic 4.0 mix^[11], and in the RCA reissue of the 1957 Chicago Symphony Orchestra recording of Mussorgsky's Pictures at an Exhibition the original 3.0 (three track) recording is available ^[12].

Optical disc authoring

Optical disc Optical disc drive Optical disc authoring Authoring software Recording technologies Recording modes Packet writing
Optical media types
Blu-ray Disc (BD): BD-R, BD-RE DVD: DVD-R, DVD+R, DVD-R DL, DVD+R DL, DVD-RW, DVD+RW, DVD-RW DL, DVD+RW DL, DVD-RW2, DVD-RAM, DVD-D, HVD Compact Disc (CD): Red Book, CD-ROM, CD-R, CD-RW, 5.1 Music Disc, SACD, PhotoCD, CD Video (CDV), Video CD (VCD), SVCD, CD+G, CD-Text, CD-ROM XA, CD-i Universal Media Disc (UMD) Enhanced Versatile Disc (EVD) Forward Versatile Disc (FVD) Holographic Versatile Disc (HVD) HD DVD: HD DVD-R, HD DVD-RW, HD DVD-RAM High-Definition Versatile Disc (HDVD) High definition Versatile Multilayer Disc (HD VMD) VCDHD GD-ROM MiniDisc (MD) (Hi-MD) Laserdisc (LD) Video Single Disc (VSD) Ultra Density Optical (UDO) Stacked Volumetric Optical Disk (SVOD) Five dimensional discs (5D DVD)
Standards
Rainbow Books File systems ISO 9660 Joliet Rock Ridge El Torito Apple ISO 9660 Extensions Universal Disk Format (UDF) Mount Rainier
Further reading
History of optical storage media High definition optical disc format war
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Content

By May 2009, there were over 5500 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.^[13][14]

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 discs as audio CDs. ^[15]

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.^[16] 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.^[16]

As of May 2009, over 440 labels^[17] 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 ^[18], and the London Symphony Orchestra established their own 'LSO Live' label.^[19]

Disc reading

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. ^{[15] [9]}

Playback hardware

Hybrid Super Audio CDs (which include both a Stereo CD and a Super Audio CD layer) can be played back on CD players. To hear the Super Audio CD Stereo, and on many discs the Super Audio CD Multichannel layer, requires a Super Audio CD player.

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.^[20] 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^[7], Marantz ^[21], Pioneer ^[8] and Yamaha ^[22] 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.^[23]

SACD players are not permitted to offer an output carrying an unencrypted stream of Direct Stream Digital (DSD) ^[24]. 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.^[25]

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 multichannel high-resolution PCM audio (converted from DSD).
• Using S/PDIF will give digital stereo sound^[A] (of either the stereo track, or a down-mix of the surround track)

PS3 was capable of converting surround DSD to lossy 1.5 Mbps DTS for playback over S/PDIF using the 2.00 software. The subsequent revision removed the feature.^[26]

DSD

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,^[27] and practical limits reduce this to 50 kHz.^[9]

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.^[28] With appropriate low-pass filtering, a frequency response of 50 kHz can be achieved along with a dynamic range of 120 dB.^[9] This is about the same resolution as PCM audio with a bit depth of 20 bits and a sampling frequency of 96 kHz ^[9]. 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.^[29]

DST

To reduce the space and bandwidth requirements of 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.^[30]

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 is 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.^[31]

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

Sound quality of SACD vs CD

In the audiophile community, sound from SACD is generally considered substantially higher in quality compared to older format Red Book CD recordings. ^[32] However, in controlled listening tests over stereo reproduction subjects have not been able to tell SACD recordings from their CD-quality converted version.^[33]

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 Shizuoka and Salzburg.^[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.^[35]

See also

• Audio format
• Audio storage
• DualDisc
• Earlier attempts at higher fidelity that stayed within the CDDA standard: XRCD and HDCD.
• Later attempts at higher fidelity that stayed within the CDDA standard: DSD-CD and Blu-spec CD.

References

Bibliography

• Janssen, E.; Reefman, D. "Super-audio CD: an introduction". Signal Processing Magazine, IEEE Volume 20, Issue 4, July 2003, pp. 83–90.

External links

• Super Audio Compact Disc: A Technical Proposal, Sony (archived PDF)
• SA-CD.net Reviews of SACD releases and a discussion forum.
• SA-CD Faq
• New SACD releases Sony website.

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