Sony ATRAC кодегі және MiniDisc форматы

Audio codec

Adaptive Transform Acoustic Coding (ATRAC) is a family of proprietary audio compression algorithms developed by Sony. MiniDisc 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 perceptible loss in 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 had the extension; however, in most cases, the files would be stored in an OpenMG Audio container using the extension Previously, files that were encrypted with OpenMG had the extension, which was replaced by starting in SonicStage v2.1. Encryption is no longer compulsory as of v3.2. Other MiniDisc manufacturers such as Sharp and Panasonic also implemented their own versions of the ATRAC codec.

ATRAC was developed for Sony's MiniDisc 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 was 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 powered Connect Music Store (Sony's equivalent of iTunes and iTunes Music Store). This was partly due to low adoption of the format, with a source claiming that 90% of European Walkman users did not use ATRAC. Walkman digital 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 files the next year. ATRAC9 was designed for PlayStation audio and debuted with the PlayStation Vita. used on the original MiniDiscs was designed to be near to CD audio quality. Years later ATRAC was improved over earlier versions at similar bitrates. For comparison, CDs are encoded at 1411.2 kbit/s, and lossless encoders can encode most CDs below 1000 kbit/s, with further bitrate reduction for easier to encode content such as voice.

ATRAC algorithms were developed in close cooperation with LSI integrated circuit development engineers within Sony in order to deliver a product that could encode at high speeds and with minimal power consumption. This contrasts with other codecs developed on computers without regard for the constraints of portable hardware. This is reflected in the design of the ATRAC codecs, which emphasize processing smaller groups of samples at a time to save memory at the cost of compression efficiency and additional multiplies. These trade offs are logical for 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 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.

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 PSP console, and ATRAC CD players. 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 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 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. 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, 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.

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. FFmpeg has an implementation of an ATRAC9 decoder.