[Wylug-help] wav file quality

[James Holden]

Jim Jackson wrote:

>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
>
>
[snip]

That sounds very likely. Changing the sample rate may also end up
changing the speed and pitch of the sample though. Also, make sure you
convert the sample depth too (ie: number of bits per sample). Voice
modems often only record at 2 or 4 bits per sample, and most sound cards
can't handle that.

James