Newsgroups: comp.speech
Path: pavo.csi.cam.ac.uk!warwick!uknet!festival!leeds.ac.uk!news
From: csc5sca@gps.leeds.ac.uk (S C Arnfield)
Subject: Re: mu law to linear conversions
Message-ID: <1993Aug3.130944.29274@gps.leeds.ac.uk>
Sender: nntp@gps.leeds.ac.uk
Organization: University of Leeds, England
References:  <23kkc3$8cv@vtserf.cc.vt.edu>
Date: Tue, 3 Aug 1993 13:09:44 GMT
Lines: 27

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.
