[pulseaudio-discuss] [PATCH 0/3] resamplers

[Tanu Kaskinen]

On Sun, 2014-09-07 at 16:32 +0600, Alexander E. Patrakov wrote:
> [sent only to Tanu by mistake, resending to the list]
> 
> 07.09.2014 15:48, Tanu Kaskinen wrote:
> > On Sun, 2014-08-24 at 13:35 +0600, Alexander E. Patrakov wrote:
> >> 04.08.2014 19:29, I wrote:
> >>> Anyway, I think that the task of objectively testing the resampler
> >>> speed and quality also needs to be done, in order to provide such
> >>> justifications. Please see
> >>> http://lists.freedesktop.org/archives/pulseaudio-discuss/2014-February/019968.html
> >>> for the formulation.
> >>
> >> Now I have the tools for the basic form of quality evaluation (using a
> >> linear sine sweep). The tools can compare quality of various resamplers,
> >> including those found in proprietary operating systems. However, the end
> >> result is still not good enough to answer the question "is this
> >> resampler good enough". The (useless) answer is almost always the same:
> >> "no, here is a sine wave frequency that it either attenuates audibly or
> >> distorts audibly", even though nobody listens to e.g 18 kHz sine waves.
> >>
> >> I will test the two new resamplers among the others today.
> >
> > Do we have some kind of a conclusion about whether the soxr and
> > libavresample resamplers should be merged? If I understood correctly,
> > the libavresample resampler appears to be somehow broken, so I guess
> > that should not be merged until the brokenness is fixed.
> 
> Correct.
> 
> > Did the soxr
> > resampler end up being the best one in any of the following categories?
> >
> > 1) Best quality
> 
> The problem with this question is that there are perfect resamplers in 
> terms of perceived quality. It has no meaning to compare e.g. 
> speex-float-5 and speex-float-10 in terms of quality. Both are just 
> perfect when given a task of resampling from 44.1 to 48 kHz.
> 
> At MQ or HQ quality, soxr is perfect, too.
> 
> > 2) Fastest
> 
> Definitely not, at least at quality levels above QQ. And at QQ, I have 
> not tested, and at that level it is just a cubic interpolator. I think 
> we don't need a complex library just for cubic interpolation.
> 
> > 3) Fastest without any audible distortions
> 
> Definitely not, by a factor of 10 (over speex).
> 
> > 4) Best compromise between speed and quality
> 
> Definitely not.
> 
> > X) Some of the above when applying licensing constraints
> 
> Definitely not. The winner on all points is speex. At the quality level 
> of 5, it never creates audible distortions. And at any quality higher 
> than 2, it eats less CPU than any comparable (in terms of quality) 
> competitors.

Thank you! I'll remove this patch set from the wiki then.

> At this point, I also suggest removing libsamplerate-based resampler.

Sounds reasonable to me.

-- 
Tanu