Table of Contents
ATRAC3+ format documentation
This is not the only ATRAC3+ documentation that floats around in the internet. A mostly independently derived specification can be found at http://wiki.multimedia.cx/index.php?title=ATRAC3plus.
intro
ATRAC3+ is a hybrid subband codec like MP3. The signal is split into 16 bands, each band is then divided into two parts: A superposition of sinusodial tones and the spectral residue that is encoded in the frequency domain. For the frequency-domain encoding, some of the low frequency bands are split themself into smaller parts, called quantization units, to a total of 32 quantization units. The purpose of the quantization unit is that each unit has its own quantization parameters.
ATRAC3+ can have more than 2 channels - in that case more than one substream is present. This case is not described here.
Parsing
- First bit must be zero
- Array of blocks follows, each block:
- two bits type followed by data
- type 0 = single channel substream data
- type 1 = dual channel (stereo) substream data
- type 2 = non-audio data (ignored)
- type 3 = end of data marker
Synthesis
- Spectral residual synthesis
- Sinusodial tone synthesis
- Noise synthesis