Newsgroups: comp.speech
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From: rwdehoed@dz12.cca.rockwell.com (R.W. DeHoedt)
Subject: CCITT G.711, A-law 
Message-ID: <D45os1.D06@lazrus.cca.rockwell.com>
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Reply-To: rwdehoed@dz12.cca.rockwell.com
Organization: Rockwell International
Date: Fri, 17 Feb 1995 18:02:24 GMT
Lines: 36

I've been examining the CCITT G.711 Rec. Table 1a/b (A-Law) and
comparing it to Table 3.2, Segmented A-Law Encoding/Decoding in Digital
Telephony, Second Ed. by John Bellamy.  

In particular, the numbers listed in the code value vs. Decoder output
don't match in both tables.  They differ by 1.

The u-Law tables match!

for example,

CCITT                   Bellamy
-------------------------------------------------------------------------
4032	128		4032	127
1056	97		1056	96
 :       :                :      :

In the Bellamy book, the Setment Code S and the Quantization Code Q
together form the Code value.  In the CCITT spec, Character signal
translated to the decoder output value is off by 1 (ignoring bit 1, the
sign, and just using the magnitude bits 2 to 7).

Maybe I'm just doing something real dumb, but I just don't see it.  
Any clarfication would be appreciated.

Thanks

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Russ W. De Hoedt        Phone:  319-395-3059         \   _   /        
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