[pulseaudio-discuss] Patch review status wiki page updated

[Damir Jelić]

On Fri, Nov 29, 2013 at 06:48:02PM +0600, Alexander E. Patrakov wrote:
> 
> Thanks for the update.
> 
> Tanu: could you please add the following text to the patch status page
> regarding Damir's project, just to keep all information in one place?
> 
> """
>  * Status update:
> http://article.gmane.org/gmane.comp.audio.pulseaudio.general/18991
>  * Performance tests (mono):
> http://poljar.blogspot.com/2013/08/vol-2-resampling-methods.html
>  * Performance tests (stereo & 5.1): TBD
>  * Bandwidth & Aliasing tests: TBD, with explanatory material at
> http://poljar.blogspot.com/2013/10/epilogue-fourier-analysis-and-testing.html
>  * Features (such as variable-rate support, input & output formats,
> optimizations for particular combinations of sample rates, compatibility
> with rewinds): TBD
> """
> 
> Separate performance tests for non-mono input are needed because some
> resamplers (e.g. libsamplerate and my resampler in Wine) need to perform
> some auxiliary computation (e.g., in my case, interpolation of tabulated
> filter coefficients) once and then use the result for each channel.
> 
> The 2013-10 blog post touches upon the important topic of the resampler
> quality. Indeed, there are two important properties that are discussed in
> the blog post:
> 
>  * [Bandwidth] The resampler should not attenuate signal at frequencies that
> are below the lowest of the two Nyquist frequencies.
>  * [Aliasing] The resampler should not create anything at frequencies not
> present in the original signal.
> 
> However, that blog post only deals with one (unspecified) resampler, and
> thus is only an illustration of the above properties, but not a comparison
> of resamplers based on these properties. That's why the TBD above.
> 
> I think it would be a good idea to post a spectrogram of a resampled linear
> sweep from 0 Hz to half of the original sampling rate. The result would be
> similar to this collection of images (which compares, for 96k -> 44.1k
> resampling, the old Wine resampler, the linear-interpolation resampler, two
> of the then-proposed resamplers, and Speex at different quality settings):
> http://imgur.com/a/0w8s4
> 

There is an extensive list of spectrograms of different resamplers here
[1]. Although only the highest quality levels are tested it should be
useful in lack of own measurements (at least for now).

[1] http://src.infinitewave.ca/