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  • Extensions: au, snd
  • Company: Sun
  • MIME Types:
    • snd, au: audio/basic, audio/x-basic, or audio/x-pn-au

AU, aka SND, is a simple PCM file format used widely on Sun systems. The format consists of a header followed by the raw sample data.

The format of the header is, with all numeric fields big endian:

magic            32 bits  ".snd"
data_start       32       absolute file offset of first sample
data_size        32       size of sample data, 0 means unspecified
sample_format    32       sample format code, see below
sample_rate      32       sample rate in samples/second
channels         32       number of channels

The header may be followed by a chunk of arbitrary data if the data_start field is greater than 24.

The sample format codes are:

 0  unspecified
 1  8-bit mu-law
 2  8-bit signed linear
 3  16-bit signed linear
 4  24-bit signed linear
 5  32-bit signed linear
 6  floating-point
 7  double precision float
 8  fragmented sampled data
 9  unknown
10  DSP program
11  8-bit fixed-point
12  16-bit fixed-point
13  24-bit fixed-point
14  32-bit fixed-point
15  unknown
16  non-audio data
17  mu-law squelch
18  16-bit linear with emphasis
19  16-bit linear with compression
20  16-bit linear with emphasis and compression
21  Music Kit DSP commands
22  Music Kit DSP samples
23  G.721 ADPCM
24  G.722 ADPCM
25  G.723 ADPCM
26  5-bit G.723 ADPCM
27  8-bit a-law