[nas] NAS with XVision

[J. Thompson]

In the answer to the original question, I don't know but I suspect the
resampling is done in NAS.

I have looked at the resampling in NAS and it is a quick and dirty solution,
which is optimised for speed not audio quality. The reason for
this is that when NAS was conceived, there just wasn't the processing power in
the average workstation, let alone PC to do a reliable real-time accurate
conversion.  So your poor sound quality is probably as a result of the
conversion in NAS.

The only way to get around it is to resample your audio data before trying to
play it, or do the conversion on the fly. The resampling in SOX uses the
algorithm by Julian O. Smith III which is described in his paper.
ftp://ccrma-ftp.stanford.edu/pub/BandlimitedInterpolation.eps.Z   
I have tried this algorithm on my old 150MHz Pentium and it just about runs in
real-time under Linux and is optimised for audio quality. The difficulty then
becomes how do you pipe the output of SOX into NAS. I'm afraid you can't as the
audio I/O bits in NAS don't work with stdin, there is an fseek in the code.  So
you have to reasmple your audio files and store the resampled files before
attempting to play them, which is probably not what you want. 

I suppose the integration of this algorithm into NAS should  go on the
wish list, to improve audio quality but if anyone wants to attempt this then
they should be wary, and I'm not volunteering. The code on the Stanford website
is GPLed which is  different to the current NAS license (Please don't start a
thread on NAS licensing we visited this not long ago). There is however a way
around the license problem.  I have found that original version e.g. the one in
SOX was not GPLed, so it could be possible to strip the code out of SOX and put
it in NAS quite happily without conflicting with the current NAS license.

Jonathan Thompson

On Thu, 09 Nov 2000, Jon Trulson wrote:
>On Thu, 9 Nov 2000, Ola Andersson wrote:
>
>> Date: Thu, 09 Nov 2000 15:27:56 +0100
>> From: Ola Andersson <rand at ling.umu.se>
>> To: nas at radscan.com
>> Subject: [nas] NAS with XVision
>> 
>> Hi!
>> 
>> I using XVision under Windows which has support for NAS.
>> I can play files, but certain samplingfrequencies sounds
>> bad. XVision can only play 11025,22050 and 44100 Hz and
>> when I play 16000 Hz sounds it resamples the sound.
>> Is this resampling done by XVision or NAS?
>> 
>
>
>	I'm assuming that Xvision is the NAS 'server' side (ie: that's
>where the sounds come out).  The Server is responsible for resampling I
>believe.
>
>
>-- 
>Jon Trulson    mailto:jon at radscan.com
>ID: 1A9A2B09, FP: C23F328A721264E7 B6188192EC733962
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