Editing Super Audio CD (section)

== Technology ==

{| class="wikitable" style="float: right"
|+ SA-CD characteristics
! Characteristic
! CD layer (optional)
! SACD layer
|-
| Disc capacity
| 700{{nbsp}}MB<ref name="Middleton, Zak"/>
| 4.7{{nbsp}}GB<ref name=extremetech2001/>
|-
| Audio encoding
| 16-bit [[pulse-code modulation]]
| 1-bit [[Direct Stream Digital]]
|-
| Sampling frequency
| 44.1{{nbsp}}kHz
| 2,822.4{{nbsp}}kHz (2.8224{{nbsp}}MHz)
|-
| Audio channels
| 2 ([[stereo]])
| Up to 6 ([[surround sound|discrete surround]])
|-
| Playback time if stereo
| 80 minutes<ref name="Clifford"/>
| 110 minutes without DST compression<ref name=extremetech2001/>
|}

SACD discs have identical physical dimensions as standard compact discs. The [[Areal density (computer storage)|areal density]] of the disc is the same as a [[DVD]].  There are three types of disc:<ref name=extremetech2001/>

*'''Hybrid''': Hybrid SACDs have a 4.7 GB SACD layer (the ''HD layer''), as well as a CD (Red Book) audio layer readable by most conventional compact disc players.<ref name="Hybrid+SACD"/>
*'''Single-layer''': A disc with one 4.7 GB SACD layer.
*'''Dual-layer''': A disc with two SACD layers, totaling 8.5 GB, and no CD layer. Dual-layer SACDs can store nearly twice as much data as a single-layer SACD. Like most dual-layer DVDs, the data spiral for the first layer is encoded from the inside out, and the second layer is encoded starting from the point where the first layer ends and ending at the innermost part of the disc.{{citation needed|date=March 2022}} Unlike hybrid discs, both single- and dual-layer SACDs are incompatible with conventional CD players and cannot be played on them.

A stereo SACD recording has an uncompressed rate of 5.6&nbsp;[[Mbit/s]], four times the rate for [[Red Book (audio CD standard)|Red Book]] CD stereo audio.<ref name="extremetech2001"/>

Commercial releases commonly include both surround sound (five full-range plus [[Low-frequency effects|LFE]] multi-channel) and stereo (dual-channel) mixes on the SACD layer.{{citation needed|date=October 2013}} Some reissues retain the mixes of earlier multi-channel formats (examples include the 1973 [[quadraphonic]] mix of [[Mike Oldfield]]'s ''[[Tubular Bells]]'' and the 1957 three-channel stereo recording by the [[Chicago Symphony Orchestra]] of [[Mussorgsky]]'s ''[[Pictures at an Exhibition]]'', reissued on SACD in 2001 and 2004 respectively).

=== Disc reading ===
[[file:Sacd.svg|thumb|A hybrid Super Audio CD uses two layers and the standardized [[focal length]] of conventional CD players to enable both types of player to read the data]]

Objective lenses in conventional CD players have a longer working distance, or [[focal length]], than lenses designed for SACD players. In SACD-capable DVD, Blu-ray and Ultra HD Blu-ray players, the red DVD laser is used for reading SACDs.{{citation needed|date=March 2022}} This means that when a hybrid SACD is placed into a conventional CD player, the infrared laser beam passes through the SACD layer and is reflected by the CD layer at the standard 1.2&nbsp;mm distance, and the SACD layer is out of focus. When the same disc is placed into an SACD player, the red laser is reflected by the SACD layer (at 0.6&nbsp;mm distance) before it can reach the CD 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 SACD layer.<ref name=extremetech2001/><ref name="muszeroldal"/>

=== Direct Stream Digital ===
{{Main|Direct Stream Digital}}

SACD audio is stored in [[Direct Stream Digital]] (DSD) format using [[pulse-density modulation]] (PDM) where audio amplitude is determined by the varying proportion of 1s and 0s. This contrasts with [[compact disc]] and conventional computer audio systems using [[pulse-code modulation]] (PCM) where audio amplitude is determined by numbers encoded in the bit stream. Both modulations require neighboring samples to reconstruct the original waveform; the more neighboring samples, the lower the frequency that can be encoded.

DSD is [[1-bit DAC|1-bit]], has a sampling rate of 2.8224&nbsp;[[MHz]], and makes use of [[noise shaping]] [[Quantization (signal processing)|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&nbsp;[[decibel|dB]] from 20&nbsp;Hz to 20&nbsp;kHz and an extended frequency response up to 100&nbsp;kHz, although most available players list an upper limit of 70–90&nbsp;kHz,<ref name="Reefman"/> and practical limits reduce this to 50&nbsp;kHz.<ref name=extremetech2001/> Because of the nature of [[Delta-sigma modulation|sigma-delta converters]], DSD and PCM cannot be directly compared. DSD's frequency response can be as high as 100&nbsp;kHz, but frequencies that high compete with high levels of ultrasonic [[quantization noise]].<ref name="ambisonic2001"/> With appropriate [[low-pass filter]]ing, a [[frequency response]] of 20&nbsp;kHz can be achieved along with a dynamic range of nearly 120&nbsp;dB, which is about the same dynamic range as PCM audio with a resolution of 20 bits.{{citation needed|date=August 2013}}

=== Direct Stream Transfer ===

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. It 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.<ref name="direct-stream-digital"/>

Direct Stream Transfer compression was standardized as an amendment to the [[MPEG-4 Audio]] standard, [[ISO/IEC]] 14496-3:2001/Amd 6:2005 (Lossless coding of oversampled audio), in 2005.<ref name="dst-iso"/><ref name="dst-iso2"/> It contains the DSD and DST definitions as described in the Super Audio CD Specification.<ref name="dst-iso-ipsj"/> The MPEG-4 DST provides lossless coding of oversampled audio signals. Target applications of DST are archiving and storage of [[1-bit DAC|1-bit]] oversampled audio signals and SA-CD.<ref name="dst-chiariglione"/><ref name="dst-chiariglione-old"/><ref name="mpeg4audio-version4-2009"/>

A [[reference implementation]] of MPEG-4 DST was published as ISO/IEC 14496-5:2001/Amd.10:2007 in 2007.<ref name="dst-reference-implementation"/><ref name="dst-reference-implementation-iso"/>

=== Copy protection ===

SACD has several [[copy protection]] features at the physical level, which made the digital content of SACD discs difficult to copy until the [[PlayStation 3 Jailbreak|jailbreak of the PlayStation 3]]. The content may be copyable without SACD quality by resorting to the [[analog hole]], or ripping the conventional 700&nbsp;MB layer on hybrid discs. Copy protection schemes include physical pit modulation and 80-bit [[encryption]] of the audio data, with a key encoded on a special area of the disc 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, and SACDs can only be manufactured at the disc replication facilities in [[Shizuoka Prefecture|Shizuoka]] and [[Salzburg]].<ref name="sa-cd-net-news"/><ref name="dvddemystified"/> 

Nonetheless, very early versions of the [[PlayStation 3]] with an SACD-compatible drive and appropriate firmware<ref>{{Cite web |title=How Sony's PlayStation 3 could save your SACD collection |url=https://www.gramophone.co.uk/features/article/how-sony-s-playstation-3-could-save-your-sacd-collection |access-date=2024-11-28 |website=Gramophone |language=en}}</ref> and certain Blu-ray players<ref>{{Cite web |date=2016-07-20 |title=SACD Ripping using an Oppo or Pioneer? Yes, it's true! |url=https://audiophilestyle.com/forums/topic/28569-sacd-ripping-using-an-oppo-or-pioneer-yes-its-true/ |access-date=2024-11-28 |website=Audiophile Style |language=en-US}}</ref><ref>{{Cite web |date=2018-09-06 |title=Music in the Round #93: miniDSP & Ripping SACDs Page 2 |url=https://www.stereophile.com/content/music-round-93-minidsp-ripping-sacds-page-2 |access-date=2024-11-28 |website=Stereophile.com |language=en}}</ref> can use specialized software to extract a [[Direct Stream Digital|DSD]] copy of the HD stream.