Adaptive Transform Acoustic Coding - China handheld gps navigators - car navigators

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General bitrate quality

ATRAC's original 292 kbit/s bitrate was designed to be close to CD quality acoustically. This is the bitrate used on original MiniDiscs. 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 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 compression efficiency and additional multiplies. These trade-offs are entirely logical on DSP systems, where memory is often at a premium compared to multiplier performance.

Sony Walkmans offer better battery life when playing ATRAC files as compared to MP3 files. However, 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.

ATRAC1

ATRAC1 was first used in Sony's own theater format SDDS 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 is 292 kbit/s.

Quality is generally transparent for many people (meaning that it is not possible to tell an ATRAC encoding from the source).[citation needed] This is most possible when using the latest algorithm, Type-S, or Type-R (Type-S only improves LP modes). Like most other audio compression codecs, some signals will "trip" the codec and cause artifacts, though these are not usually severe enough to be obvious.

High-frequency 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 (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-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 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 in order to try and 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-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.

FFmpeg has an implementation of an ATRAC3 decoder, which was converted to fixed precision and implemented in the Rockbox series of firmwares for ARM, Coldfire and MIPS processors. RealAudio8 is an implementation of ATRAC3.

The PlayStation3 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 mixing.

ATRAC3plus

ATRAC3plus CD playing on a Sony car stereo.

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 thought to be a hybrid subband/MDCT codec, though not much information has been released. It uses a relatively large transform window of 4096 samples, four times bigger than that of ATRAC3, it also uses Generalized Harmonic Analysis (GHA). The signal is split into 16 sub-bands before MDCT and bit allocation.

In the recently released SonicStage version 3.2 and 3.3 some more bitrates have been introduced, 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 MP3 at 128 kbit/s, or AAC at 96 kbit/s.

ATRAC Advanced Lossless

ATRAC Advanced Lossless (AAL) is the latest update to the codec family. It can provide compression for a CD music source at approximately 3080% that of the original size without any quality loss.

ATRAC Advanced Lossless is one of the very few audio codecs in the market that can provide scalable compression. It records both the information of ATRAC3 and ATRAC3plus, the residual information that ATRAC3 or ATRAC3plus eliminated from original signal. The ATRAC3 or ATRAC3plus data can be extracted just as it is, or the eliminated information can be added to perfectly reproduce the information on the original CD. In other words, ATRAC Advanced Lossless only requires storing one type of data, eliminating the need of data recompression and allowing the file size to be smaller than uncompressed or compressed versions of the same file. Benefits of scalable compression include providing excellent backward compatibility as well as faster transfer speed between portable audio devices and PC.

Similar "core" and "residual" stream implementations have also been used in the free software codec WavPack and DTS-HD Master Audio.

ATRAC Advanced Lossless is widely supported in older Walkman players and SonicStage version 4 or later. Sonic Stage 4 allows download of ATRAC Advanced Lossless to Minidisc Players, PlayStation Portable,and Playstation 3. Currently the latest Walkman players do not support ATRAC Advanced Lossless/ATRAC. Sony has all but dropped the ATRAC related codecs in the USA and Europe and their SonicStage powered 'Connect' Music Service (Sony's equivalent of iTunes) on 31 March 2008. However, it is being continued in Japan and various other countries. From September 2007 Sony now only manufactures in USA and Europe one Walkman product that supports ATRAC Advanced Lossless downloads/ATRAC, a portable minidisc player.

See also

Lossy data compression

OpenMG

SonicStage

Walkman

References

^ Siliconvalley.com

^ Sony Global - ATRAC - Developer's Interview

^ Source code for ATRAC decoder

^ rjamorim.com

^ Source code for ATRAC3 decoder

^ Develop game magazine article

^ ITS test report

External links

ATRACLife.com - This domain is now parked, forum content only available from google cache.

News portal, discussion forums and downloads related to ATRAC.

Sony.net, ATRAC technology page.

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Multimedia compression formats

Video compression

ISO/IEC

MJPEG  Motion JPEG 2000  MPEG-1  MPEG-2 (Part 2)  MPEG-4 (Part 2/ASP  Part 10/AVC)  HVC

ITU-T

H.120  H.261  H.262  H.263  H.264  H.265

Others

AMV  AVS  Bink  CineForm  Cinepak  Dirac  DV  Indeo  OMS Video  Pixlet  RealVideo  RTVideo  SheerVideo  Smacker  Sorenson Video  Theora  VC-1  VP6  VP7  VP8  WMV   XVD

Audio compression

ISO/IEC

MPEG-1 Layer III (MP3)  MPEG-1 Layer II  MPEG-1 Layer I  AAC  HE-AAC  MPEG-4 ALS  MPEG-4 SLS  MPEG-4 DST

ITU-T

G.711  G.718  G.719  G.722  G.722.1  G.722.2  G.723  G.723.1  G.726  G.728  G.729  G.729.1

Others

AC3  AMR  AMR-WB  AMR-WB+  Apple Lossless  ATRAC  DRA  FLAC  GSM-FR  GSM-EFR  iLBC  Monkey's Audio  -law  Musepack  Nellymoser  OptimFROG  RealAudio  RTAudio  SHN  SILK  Siren  Speex  TwinVQ  Vorbis  WavPack  WMA  True Audio

Image compression

ISO/IEC/ITU-T

JPEG  JPEG 2000  JPEG XR  lossless JPEG  JBIG  JBIG2  PNG  WBMP

Others

APNG  BMP  DjVu  EXR  GIF  ICER  ILBM  MNG  PCX  PGF  TGA  TIFF

Media containers

General

3GP  ASF  AVI  Bink  DMF  DPX  EVO  FLV  GXF  M2TS   Matroska  MPEG-PS  MPEG-TS  MP4  MXF   Ogg  QuickTime  RealMedia  RIFF  Smacker  VOB

Audio only

AIFF  AU  WAV

See Compression methods for methods and Compression software implementations for codecs

Categories: Audio codecsHidden categories: All articles with unsourced statements | Articles with unsourced statements from February 2007

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This article was published on 2011/04/22