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- Path: sparky!uunet!pipex!demon!cix.compulink.co.uk!rspence
- Newsgroups: comp.dsp
- From: rspence@cix.compulink.co.uk (Richard Spence)
- Subject: Format of .AU Sound files
- Cc: rspence@cix.compulink.co.uk
- Reply-To: rspence@cix.compulink.co.uk
- Date: Thu, 31 Dec 1992 13:32:00 +0000
- Message-ID: <memo.834974@cix.compulink.co.uk>
- Sender: usenet@demon.co.uk
- Lines: 37
-
- christos@kuhub.cc.ukans.edu () writes:
-
- > Hello there,
-
- > I am using the Public Domain program Sound Tools on the Sun station
- > to record speech. The speech samples are saved in a mu-law 8bits/sample
- > encoding rule with a standard ".au" header precceding the data. What I
- > would like to know is what the format of the speech samples is? In other
- > words, I am reading the bytes that correspond to 8-bit speech samples but I
- > don't know whether they are in signed binary format(2's complement) or
- > unsigned binary format or anyother format. I have tried both binary signed
- > (2' complement) and unsigned but it doesn't work. Does anybody know how the
- > samples are stored?
-
- > I would appreciate any relevant response.
-
- The most likely encoding will be a standard telecomms encoding at 64kbps or
- 8kHz audio. One second of information will be 8000 bytes, not 8kbytes.
-
- The 'original' samples are 12 bits wide and a compression algorithm is
- applied to get down to 8 bits. The USA (and dependants) use the mu-law
- encoding scheme. We Europeans use an A-law scheme.
-
- So much for background. If I remember correctly, the most significant bit is
- a sign bit, indicating positive (0) or negative (1) value. The remaining 7
- bits are the encoded amplitude of the sample. Manipulation will require you
- to decode the sample correctly, and I don't have the details of mu-law
- encoding to hand. But, I know where it is described. Try and get hold of the
- CCITT's G.7xx series recommendations which is one large volume. Try a
- technical library of a university. Alternatively, you could ask very nicely
- and I will try to mail the relevant pages when I'm over in the US in January.
-
- Richard Spence
- rspence@cix.compulink.co.uk
- CompuServe: 100112,304
-
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