Editing ATRAC (section)

== Formats ==
=== ATRAC (1) (versions 1.0–4.5, Type R/S) ===
ATRAC1 was first used in Sony's own theater format [[Sony Dynamic Digital Sound|SDDS]] system in the 1990s, and in this context is a direct competitor to [[Dolby Digital#Dolby Digital|Dolby Digital (AC3)]] and [[DTS (sound system)|DTS]]. SDDS uses ATRAC1 with 8 channel encoding, and with a total encoding rate over all the channels of 1168&nbsp;kbit/s.

Two stacked [[quadrature mirror filter]]s split the [[Signal (information theory)|signal]] into 3 parts:
* 0 to 5.5125&nbsp;kHz
* 5.5125 to 11.025&nbsp;kHz
* 11.025 to 22.05&nbsp;kHz

Full [[stereophonic sound|stereo]] (i.e., independent channel) encoding with a data rate of 292&nbsp;kbit/s.

High-[[frequency]] lowpass depends on the complexity of the material; some encodings have content clear up to 22.05&nbsp;kHz.

ATRAC1 can also be used in [[Monaural|mono]] (one channel) mode, doubling recording time.

[[FFmpeg]] has an implementation<ref>{{Cite web|url=http://git.ffmpeg.org/?p=ffmpeg;a=blob;f=libavcodec/atrac1.c;hb=HEAD|archive-url=https://web.archive.org/web/20110726052149/http://git.ffmpeg.org/?p=ffmpeg%3Ba%3Dblob%3Bf%3Dlibavcodec%2Fatrac1.c%3Bhb%3DHEAD|url-status=dead|title=Source code for ATRAC decoder|archive-date=26 July 2011}}</ref> of an ATRAC1 decoder.

=== ATRAC3 (LP2 and LP4 Modes) ===
Like ATRAC1 and MP3, ATRAC3 is also a hybrid [[Sub-band coding|subband]]-[[Modified discrete cosine transform|MDCT]] encoder, but with several differences.

In ATRAC3, Three stacked QMF split the signal into 4 parts:
* 0 to 2.75625&nbsp;kHz (DC to ''f''/16)
* 2.75625 to 5.5125&nbsp;kHz (''f''/16 to ''f''/8)
* 5.5125 to 11.025&nbsp;kHz (''f''/8 to ''f''/4)
* 11.025 to 22.05&nbsp;kHz (''f''/4 to ''f''/2)

The four [[Sub-band coding|subbands]] are then MDCT encoded using a fixed-length transform. Unlike nearly all modern formats, the transform length cannot be varied to optimize coding transients. Instead, a simpler transient encoding technique called [[gain control]] is used, in which the gain of different subbands is varied during a transient prior to MDCT and then restored during decoding after the inverse MDCT to try to smooth over transients. Additionally, prior to [[Quantization (signal processing)#Quantization and data compression|quantization]], tonal components are subtracted from the signal and independently quantized. During decoding, they are separately reconstructed and added back to reform the original MDCT coefficients.

Sony claims the major advantage of ATRAC3 is its coding efficiency, which was tuned for portable DSP which provides less computing power and battery life. However, as ATRAC is a hybrid [[Sub-band coding|subband]]-[[Modified discrete cosine transform|MDCT]] codec that is algorithmically very similar to [[MP3]], any advantage is probably exaggerated. Compared to newer formats such as [[Vorbis|Ogg Vorbis]] which use a simple MDCT rather than a hybrid, ATRAC3 must perform an additional computationally expensive inverse-[[Quadrature mirror filter|QMF]], although the hybrid system significantly reduces memory usage, which was likely a factor given the limited memory available when ATRAC was first developed.

;LP2 Mode
This uses a 132&nbsp;kbit/s data rate, the quality of which is advertised to be similar to that of [[MP3]] encoded at a similar bit rate.
However, in an independent [[double-blind]] test (2004/05) without format encoding parameters reference against [[Vorbis|Ogg Vorbis]], [[Advanced Audio Coding|AAC]], and [[LAME]] VBR [[MP3]], ATRAC3 came last.<ref>{{Cite web|url=http://listening-tests.freetzi.com/html/Multiformat_128kbps_public_listening_test_results.htm|title=Results of Multiformat at 128kbit/s Listening Test|website=listening-tests.freetzi.com}}</ref> 

;LP4 Mode

This reduces the data rate to 66&nbsp;kbit/s (half that of LP2), partly by using joint stereo coding and a [[Low-pass filter|lowpass filter]] around 13.5&nbsp;kHz. It allows 324 minutes to be recorded on an 80-minute MiniDisc, with the same padding required as LP2.

;Notes

[[FFmpeg]] has an implementation<ref>{{Cite web|url=http://git.ffmpeg.org/?p=ffmpeg;a=blob;f=libavcodec/atrac3.c;hb=HEAD|archive-url=https://web.archive.org/web/20110726052201/http://git.ffmpeg.org/?p=ffmpeg%3Ba%3Dblob%3Bf%3Dlibavcodec%2Fatrac3.c%3Bhb%3DHEAD|url-status=dead|title=Source code for ATRAC3 decoder|archive-date=26 July 2011}}</ref> of an ATRAC3 decoder, which was converted to [[fixed precision]] and implemented in the [[Rockbox]] series of firmware for [[ARM architecture|ARM]], [[Freescale ColdFire|Coldfire]] and [[MIPS architecture|MIPS]] processors. RealAudio8 is a high-bitrate implementation of ATRAC3 (up to 352.8kbit/s). Atracdenc is an open source implementation of ATRAC3 compatible encoder which also can use RealAudio container.

The [[PlayStation 3]] video game ''[[Race Driver: Grid]]'' uses 224 simultaneous streams of ATRAC3 compressed audio, with between one and eight channels per stream at sample rates between 24 and 48&nbsp;kHz, each filtered using 512 frequency bands of adaptive equalisation, routed via six reverb units running on the same SPU co-processor (one of eight on the PS3's Cell chip), alongside 7.1 channel hybrid third-order [[Ambisonic]] mixing.<ref>{{Cite web|url=https://issuu.com/develop/docs/dev86_web|title=Develop - Issue 86 - August 2008|website=Issuu|date=14 August 2008 }}</ref>

=== ATRAC3plus ===
[[File:Atrac3plus logo.svg|frameless|right|upright=1]]
This [[codec]] is used in Sony [[Hi-MD]] [[Walkman]] devices (e.g., "Hi-LP and Hi-SP"), Network [[Walkman]] players, [[Memory Stick]] players, [[VAIO]] Pocket, [[PS3]] and [[PlayStation Portable|PSP]] console, and [[ATRAC CD]] players. It is a hybrid subband/[[Modified discrete cosine transform|MDCT]] codec based on a 16 channel [[Quadrature mirror filter|QMF]] followed by a 128-point [[Modified discrete cosine transform|MDCT]]. Prior to MDCT coding, Generalized Harmonic Analysis (GHA) is used to extract tonal components, an improved version of the process used in ATRAC3. As in previous ATRAC versions, gain control is used to control preecho rather than variable sized transforms, although different MDCT windows are apparently possible.

[[File:Car stereo display.jpg|thumb|250px|An [[ATRAC CD|ATRAC3plus CD]] playing on a Sony car stereo.]]
[[SonicStage]] version 3.4, released in February 2006,<ref>{{Cite web|url=http://www.sony.jp:80/products/overseas/contents/support/download/index.html|title=Overseas Model Customer Support|date=7 April 2006|archive-url=https://web.archive.org/web/20060407092514/http://www.sony.jp/products/overseas/contents/support/download/index.html|archive-date=2006-04-07|access-date=2021-08-30|url-status=live}}</ref> introduced ripping CDs in bitrates 320 and 352.<ref>{{Cite web|url=https://www.sony.jp/products/overseas/contents/support/download/e_jeb_SS34ug.html|title=Overseas Model Customer Support|date=5 February 2006|archive-url=https://web.archive.org/web/20060205040106/https://www.sony.jp/products/overseas/contents/support/download/e_jeb_SS34ug.html|archive-date=2006-02-05}}</ref> The available bitrates are: 48, 64, 96, 128, 160, 192, 256, 320 and 352&nbsp;kbit/s. The newer bitrates are not always compatible with all older hardware decoders, however, some of the older hardware has been found to be compatible with certain newer ATRAC3plus bitrates.

MiniDiscs recorded in this format are incompatible with older players.

In a test conducted by an independent firm, but financed by Sony, it was concluded that ATRAC3plus at 64&nbsp;kbit/s is equal in subjective sound quality to an obsolete MP3 encoder at 128&nbsp;kbit/s.<ref>{{Cite web|url=http://www.sony.net/Products/ATRAC3/tech/ITS_test_report.pdf |archive-url=https://web.archive.org/web/20060405031225/http://www.sony.net/Products/ATRAC3/tech/ITS_test_report.pdf |archive-date=2006-04-05 |url-status=live|title=ITS test report}}</ref> Performance against modern high quality MP3 encoders was not evaluated.

=== ATRAC Advanced Lossless ===

'''ATRAC Advanced Lossless''' is a "scalable" lossless audio codec that records a lossy ATRAC3 or ATRAC3plus stream, and supplements it with a stream of correction information stored within the file itself that allows the original signal to be reproduced, if desired. A player/decoder can extract and use just the ATRAC3 or ATRAC3plus data, or it can combine that with the correction stream to perfectly reproduce the original audio information. This allows the file to be decoded as either lossless or lossy. It is implemented in such a way that allows the file size to be smaller than uncompressed or compressed versions of the same file. Compression is approximately 30–80% of the original file. Benefits of scalable compression include providing backward compatibility, such that older devices that are not AAL-aware can still have the ATRAC3 stream available for playback without understanding the AAL format, and faster transfer speed between portable audio devices and PC.<ref>{{Cite web|url=https://www.sony.net/Products/ATRAC3/tech/aal.html|title=Sony Global - ATRAC - ATRAC Advanced Lossless|website=www.sony.net}}</ref>

ATRAC Advanced Lossless is widely supported in older [[Walkman]] players and SonicStage version 4 or later. SonicStage 4 allows download of ATRAC Advanced Lossless to MiniDisc Players, [[PlayStation Portable]], and [[PlayStation 3]]. Recent Walkman players do not support ATRAC Advanced Lossless/ATRAC.

AAL's use of a "core" (lossy) and "residual" (correction) stream is similar to the idea behind [[Opus (audio format)|Opus]], [[MPEG-4 SLS]], [[DTS-HD Master Audio]], [[Dolby TrueHD]] and Ogg Vorbis [[bitrate peeling]]. In fact, AAL was the first to be released in the commercial market with this scheme for backward compatibility.

[[WavPack]] hybrid mode and [[OptimFROG]] DualStream are in the same category, but store the correction stream in a separate file.

=== ATRAC9 ===
According to Sony ATRAC9 is a high-compression audio codec optimized for games, offering low delay (granularity) and low CPU and memory usage.
It is used in the [[PS5]], [[PS4]] and [[PS Vita]] consoles. Audio middleware such as [[FMOD]] and [[Audiokinetic Wwise]] supports it.<ref>{{cite web|title=FMOD sound formats|url=https://www.fmod.com/resources/documentation-api?page=content/generated/FMOD_SOUND_TYPE.html#/|access-date=26 March 2018}}</ref><ref>{{cite web|title=include/AK/SoundEngine/Platforms/PS4/AkTypes.h File Reference|url=https://www.audiokinetic.com/library/edge/?source=SDK&id=include%2FAK%2FSoundEngine%2FPlatforms%2FPS4%2FAkTypes.h|access-date=26 March 2018}}</ref>

[[FFmpeg]] has an implementation<ref>{{Cite web|url=https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/atrac9dec.c|title=Source code for ATRAC9 decoder|website=[[GitHub]] }}</ref> of an ATRAC9 decoder.