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). 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.
Read more about this topic: Adaptive Transform Acoustic Coding