[Wylug-help] wav file quality

[Jim Jackson]

On 8 Sep 2003, don wrote:

> I still haven't solved the problem. Setting the levels doesn't make any
> difference. But I've tried a good .wav file and it sounds ok.
>
> The audio starts off as an rmd file from the modem and it's converted to
> wav format by the line below.
>
> rmdtopvf -16 $MESSAGE | pvfspeed -s 7200 | pvftowav -16 >$WAVFILE

Ah so the linux box isn't digitising the call, the modem is and uploading
it to the linux box? If a good WAV file sounds ok then your sound is setup
right on your linux box, and the sound is either distorted at source (i.e.
in the original rmd) or distortion is introduced in the conversion
process.

What sound card do you have? And why did you choose 7200 samples per sec?
Try a more common sample rate like 8000, 11025, 16000, 22050 and see what
it sounds like. Some sound cards can only do a limited range of samplerate
playback.

Jim


> On Tue, 2003-09-02 at 12:09, Jim Jackson wrote:
> >
> > On 2 Sep 2003, don wrote:
> >
> > > I've just set up a linux telephone answering machine. But when I replay
> > > the messages either with sox or xmms the quality is awful. I've tried
> > > all of the different formats but none of them improve things. I think
> > > that there may be issues with 8 bit samples from some of the comments on
> > > the web.
> > >
> > > If I play the same wav file with windows software it sounds ok (well, as
> > > good as 2 bit samples are going to).
> > >
> > > Anybody know how to solve this?
> > >
> >
> > First off identify where the problem is. Have you played a known good
> > wav file from another source?
> >
> > Is the quality any good?
> >
> > If not then, then there's a problem with the sound play back.
> > Using a mixer controller have you shut off all unused inputs, have you
> > played with the various volume controls to find the optimum low noise
> > settings?
> >
> > If quality is good, then it's the recording side. Have you fully adjusted
> > the mixer settings for optimum record level (NOT highest!  otherwise you
> > overload the ADC and get distortion - the optimum level such that usual
> > levels are recorded with a peak of about half the maximum possible so that
> > slightly louder noises don'tr cause clipping and distortion.).
> >
> > Jim
> >
> >
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> > Wylug-help at wylug.org.uk
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> >
>
>
>
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