XA (CD-ROM Voice Data)
ADPCM audio data in the CD-ROM XA format.
| Extension | .XA |
|---|---|
| Created by | RAW2XA |
Overview
XA is the PlayStation CD-ROM XA voice data format, and its typical extension in DOS is ".XA". The format is based on the CD-ROM XA System Description of May 1991, and the XA file output by RAW2XA has a sub-header.1
The PlayStation plays back ADPCM audio data as specified in the CD-ROM XA (eXtended Audio) standard, which Sony calls XA-ADPCM audio. XA-ADPCM audio is sent directly from the CD-ROM decoder to the SPU without using main memory. Four types are supported:2
| Sampling frequency | Stereo/monaural |
|---|---|
| 37.8 kHz | Stereo |
| 37.8 kHz | Monaural |
| 18.9 kHz | Stereo |
| 18.9 kHz | Monaural |
Interleave
When XA-ADPCM audio is played back, its sectors must be interleaved with gap sectors on the CD-ROM. The ratio of data sectors to gap size depends on the type of audio and on the playback speed of the CD-ROM. In the table below a lower sampling frequency or a monaural sound therefore takes one audio sector in a longer run of sectors.23
| CD-ROM playback speed | Type | Data/gap ratio |
|---|---|---|
| Double speed | 37.8 kHz, stereo | 1 sector/7 sectors |
| Double speed | 37.8 kHz, monaural | 1 sector/15 sectors |
| Double speed | 18.9 kHz, stereo | 1 sector/15 sectors |
| Double speed | 18.9 kHz, monaural | 1 sector/31 sectors |
| Standard speed | 37.8 kHz, stereo | 1 sector/3 sectors |
| Standard speed | 37.8 kHz, monaural | 1 sector/7 sectors |
| Standard speed | 18.9 kHz, stereo | 1 sector/7 sectors |
| Standard speed | 18.9 kHz, monaural | 1 sector/15 sectors |
STR streaming data with audio places movie data in the gap sectors.3