Snd0.at9

Adaptive Transform Acoustic Coding (ATRAC) is a family of proprietary audio compression algorithms developed by Sony.

Audio middleware such as FMOD and Audiokinetic Wwise support it.

Background Music

• Sampling Frequency: 48kHz
• Number of channels: 1 or 2 (even when ATRAC9 itself supports mono, stereo, 4.0, 5.1 and 7.1)
• Limitations: maximum 2MB filesize (similar to PS Vita).

• http://gs2-sec.ww.prod.dl.playstation.net/gs2-sec/appkgo/prod/CUSA00001_00/1/i_f10c33e5f30e3b3900a201af324a2a0e3912e843c1090d66e13f378151c1afa1/i/snd0.at9 sample

Format ATRAC9

Offset	Size	Example	Value (conversion)	Notes
RIFF chunk descriptor
0x00	0x04	52 49 46 46	"RIFF"	Magic
0x04	0x04	20 B3 18 00	00 18 B3 20	File Size
0x08	0x04	57 41 56 45	"WAVE"	ID
fmt sub-chunk
0x0C	0x04	66 6D 74 20	"fmt "	chunk specifying the data format
0x10	0x04	34 00 00 00	52 bytes	fmt chunk size
0x14	0x02	FE FF	FF FE	format tag
0x16	0x02	02 00	2	Number of channels
0x18	0x04	80 BB 00 00	48000 (0xBB80)	48 kHz Sample Frequency Supported (kHz) 12 24 48 kHz
0x1A	0x04	00 00 50 46	18000	Byte rate: 144 kbps (18000/125 bytes per second) Block Align (384) * Sampling Frequency (48000) / Samples per block (1024) = 18000 Supported (kilobits per second) PS4 48 60 72 84 96 120 144 168 192 240 288 300 336 360 420 504 PSVITA 48 60 72 84 96 120 144 168 192
0x20	0x02	80 01	384	Audio block align
0x22	0x02	00 00	0	Quantifying bit number
0x24	0x02	22 00	34	Extension number
0x26	0x02	00 04	1024	Samples per block
0x28	0x04	03 00 00 00	0x03 (00000011)	Channel Mask (position of the speakers)
0x2C	0x10	-	-	Codec identifier: GUID
0x3C	0x04	01 00 00 00	-	Version

References:

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Grey literature:

• http://www.minidisc.org/aes_atrac.html