Adaptive Transform Acoustic Coding
ATRAC stands for Adaptive Transform Acoustic Coding (German as: Adaptive Tonumwandlungskodierung ) and provides an audio data compression method is.
technology
ATRAC is based on basic psychoacoustic rules and compresses audio files to a fraction of the original data volume. The ATRAC codec was introduced by Sony with the introduction of the MiniDisc in 1992 and has been subject to an increased process of further development from the start. Few other manufacturers of their own ATRAC versions are, for example, Sharp or Panasonic, which, however, placed less value on the further development of ATRAC than Sony. The reason for the low interest of other manufacturers in ATRAC is assumed to be high license fees. Because of the sound properties of "foreign" ATRAC versions (which are roughly on par with Sony's ATRAC 4.5), it is recommended to record in DSP Type-R or Type-S in order to achieve the greatest possible transparency .
construction
The ATRAC codec works with three frequency bands from 0 to 5.5 kHz, from 5.5 kHz to 11 kHz and from 11 kHz to 22 kHz, each of which is subdivided into 128 bands using MDCT . There is a block mode of 11.6 ms and a mode consisting of three short blocks of 2.9 ms, 2.9 ms and 1.45 ms. All versions of ATRAC (1.0 up to DSP Type-S) are encoded at 292 kbit / s, including the mono recording "LP" (which only contains one instead of both stereo channels and therefore only takes up half of the storage space.) ATRAC3, on the other hand, offers quality levels of 132 kbit / s "LP2" and 66 kbit / s "LP4", later also 105 kbit / s through SonicStage (also referred to as "LP2".) What is striking is that LP2 only takes 132 kbit / s 146 kbit / s used. This is due to the fact that the remaining 14 kbit / s are used to simulate older MiniDisc devices that are not MDLP-capable as a normal SP file that can be played without sound.
comparison
The advantage of the codec over other formats is the possibility of uninterrupted playback and the relatively low decoding effort required for the compressed data, so that a longer battery life is possible for portable end devices. When playing, the battery life is around 20% longer than with MP3 files at the same bit rate , although ATRAC3 was rated worse than MP3 in an independent comparison test and you would therefore have to use a higher bit rate in order to achieve a similar quality (however not documented which version of ATRAC was used for this). Another disadvantage of ATRAC is that you can hardly find any music in this format. If you convert from a lossy compressed source (such as MP3) to ATRAC, the quality suffers particularly. A special feature of ATRAC is that the codec is not explicitly assigned a bit depth, which means that some MiniDisc playback and recording devices (mainly decks from various manufacturers and portable devices from Sharp) allow playback and recording in real 20 or 24 bit quality . If an analog or digital recording of a playback source was made using the CD standard with 16-bit (for analog recordings, an A / D converter with 20 or 24-bit function is required), this can also be reproduced in a correspondingly high quality (provided that the playback device also supports D / A conversion via 16-bit.)
Copy protection measures
The codec contains various copy protection mechanisms, including digital rights management since ATRAC3 . This is intended to prevent copyright infringements, but at the same time the options for using ATRAC are restricted. Sony improved this in 2006 with the release of the SonicStage 3.4 software . The copy protection can now be switched off at will and is therefore ineffective. It only remains in the case of purchased music from Sony's Connect online store .
distribution
In addition to the MiniDisc, other playback devices from Sony also support ATRAC, for example the PlayStation 3 , PlayStation Portable , audio players with flash memory, portable ATRAC CD players and all current Walkman products. It is also used in the professional film sound format SDDS (Sony Dynamic Digital Sound) to compress the data. The alternative firmware Rockbox available for various MP3 players also offers the option of playing files compressed with ATRAC.
On August 30, 2007, Sony announced that it would discontinue its online music store Connect and switch all Walkman products to the WMA format in 2008 . Since then, no more ATRAC-capable devices have appeared. Thus the further development of ATRAC was obviously stopped.
history
The fact that older Sony devices only support ATRAC, but newer devices also support MP3 , AAC and other formats, is an indication that Sony has given up the attempt to establish its own format alongside more common formats on the market. As a proprietary format, ATRAC was supposed to occupy a dominant position in the market, inseparably from the Walkmans, which have been successful to date (a similar approach can also be observed at other companies such as Apple , which also operates a closed system with the iPod and iTunes - see also closed platform ).
The consequence of this strategy was a sharp drop in sales of portable audio players that only supported ATRAC, as the necessary conversion of MP3 files to ATRAC format was too cumbersome from the consumer's point of view. It was not until 2004 that Sony gave in and launched the NW-HD3, the first MP3-compatible Walkman. All Sony digital audio players now support multiple file formats.
Versions
The following versions of the ATRAC codec have been released so far:
| ATRAC version (year of publication) | Bit rate |
|---|---|
| ATRAC-1 (MiniDisc only) (1992) | 292 kbit / s |
| ATRAC-2 (MiniDisc + SDDS) (1994) | 292 kbit / s |
| ATRAC-3 (MiniDisc only) (1995) | 292 kbit / s |
| ATRAC-3.5 (MiniDisc only) (1996) | 292 kbit / s |
| ATRAC-4 (MiniDisc only) (1996) | 292 kbit / s |
| ATRAC-4.5 (MD decks only) (1996) | 292 kbit / s |
| ATRAC3 (with MDLP) (2000) | 132/105/66 kbit / s |
| ATRAC DSP Type-R (MiniDisc only) (1998) | 292 kbit / s |
| ATRAC DSP Type-S (MiniDisc only) (2002) | 292 kbit / s |
| ATRAC3plus (2003) | 48/64/96/128/160/192/256/320/352 kbit / s |
| Atrac Advanced Lossless (2006) |
literature
- Thomas Görne: Sound engineering. Fachbuchverlag Leipzig by Carl Hanser Verlag, Munich a. a. 2006, ISBN 3-446-40198-9 .
- Roland Enders: The home recording manual. The way to optimal recordings. 3rd, revised edition, revised by Andreas Schulz. Carstensen, Munich 2003, ISBN 3-910098-25-8 .
Web links
- Official website (English)
- MiniDisc and ATRAC FAQ (English)
- MD and Hi-MD FAQ with tables on runtimes of the Atrac codecs (German)
- Article with technical details about the ATRAC codec on ITWissen.info (German)
Individual evidence
- ↑ minidisc.org, accessed July 30, 2010
- ↑ heise.de accessed on July 30, 2010