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/
