Newsgroups: comp.speech
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From: jpcampb@afterlife.ncsc.mil (Joe Campbell)
Subject: Re: mu law to linear conversions
Message-ID: <1993Aug3.144124.20966@afterlife.ncsc.mil>
Organization: The Great Beyond
References: <23kkc3$8cv@vtserf.cc.vt.edu> <D> <1993Aug3.130944.29274@gps.leeds.ac.uk>
Date: Tue, 3 Aug 1993 14:41:24 GMT
Lines: 40

In article <1993Aug3.130944.29274@gps.leeds.ac.uk>,
S C Arnfield <csc5sca@gps.leeds.ac.uk> wrote:
>In article <23kkc3$8cv@vtserf.cc.vt.edu>, bhushan@mprg1.mprg.ee.vt.edu (Bhushan Rele) writes:
>> Hi
>> I have been using the SUN workstations audio facility to record some
>> stuff and convert it into linear PCM using MATLAB for further processing
>> by a vocoder.
>> 
>> The vocoder requires minimum 13 bit quantization.
>> 
>> Since the *.au files of the SUN are 8 bit mulaw, will the conversion
>> result in a loss of precision?Should I try something else for my work
>> in the future? 
>> 
>> Thanks in advance
>> Bhushan
>> MPRG
>
>According to the man page for audio on our sparc "... u-law audio data are
>sampled at a rate of 8000 samples per second with 12-bit precision, with the
>data compressed to 8-bit samples." Therefore the u-law files never had the
>required 13bit precision needed by your vocoder. You could ignore this and
>multiply your PCM values by 2 to make them 13 bits wide (but the lsb will
>always be zero). Besides this the audio quality of sun workstations leaves
>much to be desired and I'd advise you to look elsewhere for your sampling
>such as one of the cheap 16bit PC cards advertised in many magazines. A
>sparc based option would be expensive by comparison.
>
>Simon.

Often, the more serious problem is due to the poor filtering used in
ulaw telecomm chips (such as in the SPARC2) which introduces nonlinear
distortion (switched capacitor filters :-()

Joe
-- 
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; Dr. Campbell  N3JBC  jpcampb@afterlife.ncsc.mil  74040.305@compuserve.com ;
; My opinions are mine!   Happiness = Reality - Expectations, Click & Clack ;
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