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sound.fmt
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1995-01-17
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PSIONICS FILE - SOUND.FMT
=========================
Format of Sound files
Last modified 1994-04-22
========================
Sound files hold recorded sounds, and can only be used by the Series 3a. The
sound is played at 8000 entries per second. The file uses A-Law encoding.
A sound file begins with a 32 byte header of the following form:
Offset 0 (cstr): "ALawSoundFile**"
Offset 16 (word): format version number
Offset 18 (long): number of samples in the file
Offset 22 (word): length of silence (in 1/32 seconds) to append on playback
Offset 24 (word): number of times to repeat on playback (0 and 1 both mean
play once)
The rest of the file is sound samples. Each byte is a value encoded using
A-Law to represent 13 bit values. The most significant bit is the sign, and
the other 7 bits represent a 12 bit amplitude (note that this is a sign-and-
magnitude representation, not a twos-complement one):
S000XXXX -> S0000000XXXX1
S001XXXX -> S0000001XXXX1
S010XXXX -> S000001XXXX10
S011XXXX -> S00001XXXX100
S100XXXX -> S0001XXXX1000
S101XXXX -> S001XXXX10000
S110XXXX -> S01XXXX100000
S111XXXX -> S1XXXX1000000
When encoding values, the bits marked i are ignored:
S000XXXX <- S0000000XXXXi
S001XXXX <- S0000001XXXXi
S010XXXX <- S000001XXXXii
S011XXXX <- S00001XXXXiii
S100XXXX <- S0001XXXXiiii
S101XXXX <- S001XXXXiiiii
S110XXXX <- S01XXXXiiiiii
S111XXXX <- S1XXXXiiiiiii