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Adaptive Transform Acoustic Coding (ATRAC) is a family of proprietary audio compression algorithms developed by
Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...
.
MiniDisc MiniDisc (MD) is an erasable magneto-optical disc-based data storage format offering a capacity of 60, 74, and later, 80 minutes of digitized audio. Sony announced the MiniDisc in September 1992 and released it in November of that year fo ...
was the first commercial product to incorporate ATRAC in 1992. ATRAC allowed a relatively small disc like MiniDisc to have the same running time as CD while storing audio information with minimal loss in perceptible quality. Improvements to the codec in the form of ATRAC3, ATRAC3plus, and ATRAC Advanced Lossless followed in 1999, 2002, and 2006 respectively. Files in ATRAC3 format originally have the extension, however in most cases the files would be stored in an OpenMG Audio container using the extension . Initially files that were encrypted with OpenMG had the extension, before it was replaced by starting in
SonicStage SonicStage is a discontinued software product from Sony that is used for managing portable devices when they are plugged into a computer running Microsoft Windows. It comprises a music player and library manager, similar to iTunes, Windows Media ...
v2.1. Encryption is no longer compulsory as of v3.2. Other MiniDisc manufacturers such as
Sharp Sharp or SHARP may refer to: Acronyms * SHARP (helmet ratings) (Safety Helmet Assessment and Rating Programme), a British motorcycle helmet safety rating scheme * Self Help Addiction Recovery Program, a charitable organisation founded in 199 ...
and Panasonic also implemented their own versions of the ATRAC codec.


History

ATRAC was developed for Sony's
MiniDisc MiniDisc (MD) is an erasable magneto-optical disc-based data storage format offering a capacity of 60, 74, and later, 80 minutes of digitized audio. Sony announced the MiniDisc in September 1992 and released it in November of that year fo ...
format. ATRAC was updated with version 2, then version 3, version 4, version 4.5, and Type R and Type S. The first major update was ATRAC3 (not to be confused with version 3 of original ATRAC) in 1999. ATRAC3 would be used on MiniDisc as well as the Network Walkman and Vaio Music Clip. ATRAC3plus launched in 2003 for Hi-MD, but was also compatible with some PlayStation, VAIO and Xplod devices. On 31 March 2008 Sony all but dropped the ATRAC-related codecs in the United States and Europe, and in their
SonicStage SonicStage is a discontinued software product from Sony that is used for managing portable devices when they are plugged into a computer running Microsoft Windows. It comprises a music player and library manager, similar to iTunes, Windows Media ...
powered Connect Music Store (Sony's equivalent of
iTunes iTunes () is a software program that acts as a media player, media library, mobile device management utility, and the client app for the iTunes Store. Developed by Apple Inc., it is used to purchase, play, download, and organize digital mu ...
and
iTunes Music Store The iTunes Store is a digital media store operated by Apple Inc. It opened on April 28, 2003, as a result of Steve Jobs' push to open a digital marketplace for music. As of April 2020, iTunes offered 60 million songs, 2.2 million apps, 25,000 ...
). This was partly due to low intake of the format, with a source claiming that 90% of European Walkman users did not use ATRAC. All digital Walkman players outside Japan no longer worked with ATRAC after September 2007. Until October 1, 2012, ATRAC was the only codec available to download music from mora until they transitioned to a DRM free model and began offering
FLAC FLAC (; Free Lossless Audio Codec) is an audio coding format for lossless compression of digital audio, developed by the Xiph.Org Foundation, and is also the name of the free software project producing the FLAC tools, the reference softwa ...
files the next year. ATRAC9 was designed for PlayStation audio and debuted with the PlayStation Vita.


General bitrate quality

ATRAC's original 292 kbit/s bitrate, as used on the original MiniDiscs, was designed to be close to CD quality acoustically. Years later ATRAC was improved and is generally considered better than earlier versions at similar bitrates. For purposes of comparison, CDs are encoded at 1411.2 kbit/s, and lossless encoders can encode most CDs below 1000 kbit/s, with significant bitrate reduction for easier-to-encode content such as voice.


Performance

According to ATRAC engineers, ATRAC algorithms were developed in close cooperation with LSI integrated circuit development engineers within Sony in order to deliver on a tangible product that could encode at high speeds and with minimal power consumption. This is in contrast to other codecs developed on computers with no regard for the constraints of portable hardware. This is reflected in the design of the ATRAC codecs, which tend to emphasize processing smaller numbers of samples at a time to save memory at the cost of compression efficiency and additional multiplies. These trade-offs are entirely logical on DSP systems, where memory was often at a premium compared to multiplier performance. Sony Walkmans offer better battery life when playing ATRAC files than when playing MP3 files. However, as Sony only pushed ATRAC compatibility in Sony Ericsson Walkman series phones in the Japanese market, it is not supported in GSM/
UMTS The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the In ...
market phones. Sony's Xplod series of car audio CD players support ATRAC CDs. Minidiscs with ATRAC format songs have, in the past, been supported on Eclipse brand car stereos.


Formats


ATRAC (1) (versions 1.0–4.5, Type R/S)

ATRAC1 was first used in Sony's own theater format
SDDS is a cinema sound system developed by Sony, in which compressed digital sound information is recorded on both outer edges of the 35 mm film release print. The system supports up to eight independent channels of sound: five front chann ...
system in the 1990s, and in this context is a direct competitor to Dolby Digital (AC3) and DTS. SDDS uses ATRAC1 with 8 channel encoding, and with a total encoding rate over all the channels of 1168 kbit/s. Two stacked quadrature mirror filters split the signal into 3 parts: * 0 to 5.5125 kHz * 5.5125 to 11.025 kHz * 11.025 to 22.05 kHz Full stereo (i.e., independent channel) encoding with a data rate of 292 kbit/s. High-
frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
lowpass depends on the complexity of the material; some encodings have content clear up to 22.05 kHz. ATRAC1 can also be used in
mono Mono may refer to: Common meanings * Infectious mononucleosis, "the kissing disease" * Monaural, monophonic sound reproduction, often shortened to mono * Mono-, a numerical prefix representing anything single Music Performers * Mono (Japanes ...
(one channel) mode, doubling recording time. FFmpeg has an implementation of an ATRAC1 decoder.


ATRAC3 (LP2 and LP4 Modes)

Like ATRAC1 and MP3, ATRAC3 is also a hybrid
subband In signal processing, sub-band coding (SBC) is any form of transform coding that breaks a signal into a number of different frequency bands, typically by using a fast Fourier transform, and encodes each one independently. This decomposition is ...
- MDCT encoder, but with several differences. In ATRAC3, Three stacked QMF split the signal into 4 parts: * 0 to 2.75625 kHz (DC to ''f''/16) * 2.75625 to 5.5125 kHz (''f''/16 to ''f''/8) * 5.5125 to 11.025 kHz (''f''/8 to ''f''/4) * 11.025 to 22.05 kHz (''f''/4 to ''f''/2) The four 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 Gain or GAIN may refer to: Science and technology * Gain (electronics), an electronics and signal processing term * Antenna gain * Gain (laser), the amplification involved in laser emission * Gain (projection screens) * Information gain in deci ...
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, 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
subband In signal processing, sub-band coding (SBC) is any form of transform coding that breaks a signal into a number of different frequency bands, typically by using a fast Fourier transform, and encodes each one independently. This decomposition is ...
- MDCT codec that is algorithmically very similar to MP3, any advantage is probably exaggerated. Furthermore, compared to newer formats such as Windows Media Audio which use a simple MDCT rather than a hybrid, ATRAC3 must perform an additional and computationally expensive inverse- QMF, although the hybrid system does significantly reduce memory usage, which was likely a factor given the limited memory available when ATRAC was originally developed. ;LP2 Mode This uses a 132 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 Ogg Vorbis, AAC, and LAME VBR MP3, ATRAC3 came last. Unfortunately, due to lack of transparency in ATRAC encoder versioning, it is not known if the ATRAC3 encoder tested was optimal, and subsequent investigation was inconclusive. It is possible that newer ATRAC3 encoders offer better performance. ;LP4 Mode This reduces the data rate to 66 kbit/s (half that of LP2), partly by using joint stereo coding and a lowpass filter around 13.5 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 of an ATRAC3 decoder, which was converted to
fixed precision In computing, fixed-point is a method of representing fractional (non-integer) numbers by storing a fixed number of digits of their fractional part. Dollar amounts, for example, are often stored with exactly two fractional digits, represent ...
and implemented in the Rockbox series of firmware for ARM,
Coldfire The NXP ColdFire is a microprocessor that derives from the Motorola 68000 family architecture, manufactured for embedded systems development by NXP Semiconductors. It was formerly manufactured by Freescale Semiconductor (formerly the semiconductor ...
and MIPS processors.
RealAudio8
is a high-bitrate implementation of ATRAC3 (up to 352.8kbit/s). The
PlayStation 3 The PlayStation 3 (PS3) is a home video game console developed by Sony Interactive Entertainment, Sony Computer Entertainment. The successor to the PlayStation 2, it is part of the PlayStation brand of consoles. It was first released on Novemb ...
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 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 Ambisonics is a ''full-sphere'' surround sound format: in addition to the horizontal plane, it covers sound sources above and below the listener. Unlike some other multichannel surround formats, its transmission channels do not carry speaker si ...
mixing.


ATRAC3plus

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 The PlayStation 3 (PS3) is a home video game console developed by Sony Interactive Entertainment, Sony Computer Entertainment. The successor to the PlayStation 2, it is part of the PlayStation brand of consoles. It was first released on Novemb ...
and PSP console, and ATRAC
CD players A CD player is an electronic device that plays audio compact discs, which are a digital optical disc data storage format. CD players were first sold to consumers in 1982. CDs typically contain recordings of audio material such as music or au ...
. It is a hybrid subband/ MDCT codec based on a 16 channel QMF followed by a 128-point 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.
SonicStage SonicStage is a discontinued software product from Sony that is used for managing portable devices when they are plugged into a computer running Microsoft Windows. It comprises a music player and library manager, similar to iTunes, Windows Media ...
version 3.4, released in Feb 2006, introduced ripping CDs in bitrates 320 and 352. The available bitrates are: 48, 64, 96, 128, 160, 192, 256, 320 and 352 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 kbit/s is equal in subjective sound quality to an obsolete MP3 encoder at 128 kbit/s. 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. 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 The PlayStation 3 (PS3) is a home video game console developed by Sony Interactive Entertainment, Sony Computer Entertainment. The successor to the PlayStation 2, it is part of the PlayStation brand of consoles. It was first released on Novemb ...
. Recent Walkman players do not support ATRAC Advanced Lossless/ATRAC.


Comparable technology

AAL's use of a "core" (lossy) and "residual" (correction) stream is similar to the idea behind Opus, MPEG-4 SLS, DTS-HD Master Audio, Dolby TrueHD and Ogg Vorbis
bitrate peeling Bitrate peeling is a technique used in Ogg Vorbis audio encoded streams, wherein a stream can be encoded at one bitrate but can be served at that or any lower bitrate. The purpose is to provide access to the clip for people with slower Internet ...
. 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. Used in PS5, PS4 and PS Vita consoles. Audio middleware such as FMOD and
Audiokinetic Wwise Wwise (Wave Works Interactive Sound Engine) is Audiokinetic's software for interactive media and video games, available for free to non-commercial users and under license for commercial video game developers. It features an audio authoring tool and ...
supports it.


See also

*
Lossy compression In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data si ...
* OpenMG *
SonicStage SonicStage is a discontinued software product from Sony that is used for managing portable devices when they are plugged into a computer running Microsoft Windows. It comprises a music player and library manager, similar to iTunes, Windows Media ...
* Walkman


References


External links


Sony.net
ATRAC technology page. {{Compression formats Audio codecs Sony products Audiovisual introductions in 1992 Japanese inventions