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ATRAC (Adaptive TRansform Acoustic Coding) is a family of proprietary audio compression algorithms used to store information on MiniDiscs and other Sony-branded audio players. The original ATRAC-1 was first developed by Sony in 1992; the higher compression versions known as ATRAC3 and ATRAC3plus followed in 1999 and 2002, respectively. Besides Sony, other MiniDisc manufacturers such as Sharp and Panasonic also have their own versions of the ATRAC codec. In 2006, a hybrid lossless compression scheme was added to the ATRAC family.
General bitrate quality There seems to be a general agreement that ATRAC1 usually gives transparent quality at 292 kbit/s. This is the bitrate used on original minidiscs, and the quality was usually accepted to be quite good. Later versions of ATRAC can usually be expected to be slightly better than earlier ones. ATRAC3plus probably gives transparent quality at 256 kbit/s. For purposes of comparison, CDs are encoded at around 1400 kbits/s, and lossless encoders can encode most CDs at around 1000 kbit/s with bitrate possibly going down to around 250 kbit/s or even lower for easy content. There is some disagreement about the ATRAC quality (and its variants) at the lower bitrates. Judgements of sound quality are necessarily subjective. Sony claims that ATRAC3plus gives "near CD quality" at 64 kbit/s. Unfortunately this general assertion does not specify which type of source is being encoded, as a recording of a choral symphony might be more difficult to encode at 64 KBits/s than a recording of someone talking. Bitrate quality compared to other formats Sony's official claim is that ATRAC3plus at 64 kbit/s rate provides a quality comparable to MP3 at 128 kbit/s, placing this codec in the same league as WMA (with similar claims from Microsoft). Performance According to ATRAC engineers, ATRAC familly is much more friendly regarding decoding chips than other schemes, and so would need far less processor power to decompress a stream *. Sony Walkmans offer better battery life when playing ATRAC files as compared to MP3 files. This is how the Sony NW-HDx series (NW-HD1, NW-HD3, NW-HD5) of Walkmen declare a 30-hour battery life. But, eventhough this is established, it fails to point out why Sony didn't push for ATRAC compatibility in their Sony-Ericsson Walkman series phones (W800i, W700i, W550i, W600i and so on). It would only make sense, given the prospect of longer battery life which is necessary in multimedia phones. Sony's Xplod series of car audio CD players support ATRAC CDs - relevant, but not necessary considering the almost unlimited supply of battery power that a car provides. 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: Full stereo (i.e., independent channel) encoding with a data rate is 292 kbit/s. | ||||||||
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