[linux-audio-dev] How to test resampling quality?

[James Courtier-Dutton]

Steve Harris wrote:
> On Wed, Sep 27, 2006 at 11:16:27 +0100, James Courtier-Dutton wrote:
>> Hi,
>>
>> I was wondering if there are any tools out there to test audio
>> resampling quality. I am particularly interested in 44.1kHz to 48kHz
>> resampling due to the fact that most sound cards prefer 48kHz.
>>
>> At least with up sampling (low rate to higher rate) one does not get
>> aliasing.
>>
>> I really just want to find some algorithm that I can use to compare
>> 44.1kHz audio signal with an 48kHz audio signal, and to see if there has
>> been any lose of quality during the up sample.
> 
> I'm not sure if it's a good technique, but to test my dithering algorithms
> I took high precision FFTs of the input (sine wave IIRC) and output
> signals and looked for extranous peaks. You can see the test code in the
> tarball: http://plugin.org.uk/libgdither/libgdither-0.6.tar.gz
> c.f. http://plugin.org.uk/libgdither/TESTING
> 
> - Steve

It is not quite that easy. The buckets for FFTs at 44.1kHz rate might be
different from the buckets at 48kHz rate. Some of the buckets are the
same, but not all. I.e. the 1 Hz and the 2 Hz buckets are the same, but
the buckets above 44.1kHz might be different as the 44.1kHz rate FFT
will not have baskets above 44.1kHz.

James