[pulseaudio-discuss] Resampler quality evaluation: now with room noise!

[David Henningsson]

On 2014-09-27 17:56, Alexander E. Patrakov wrote:
> 26.09.2014 02:56, David Henningsson wrote:
>>
>>
>> On 2014-09-25 21:54, Alexander E. Patrakov wrote:
>>> The conclusion of that work was that we need to use speex-float-5 to
>>> match the metric of "never introducing audible distortions" (that other
>>> operating systems meet by default) when resampling from 44.1 to 48 kHz.
>>> However, David Henningsson argued that this "never" included a lot of
>>> unrealistic worst-case conditions, i.e. that the quality achieved in
>>> proprietary OSes is actually overkill.
>>
>> To elaborate, I'm not saying they're completely unrealistic, I'm don't
>> doubt that the resampler noises are hearable in *some* environments. The
>> question is how common it is.
>>
>> We need to find a balance between quality on one side and CPU
>> consumption on the other side.
>>
>> We used to have speex-float-3 but changed to speex-float-1 because
>> distros had changed, which in turn was because people complained that PA
>> took too much CPU. So speex-float-3 was causing problems for some people.
>
> I think (but cannot claim this yet as a scientific fact) that we can
> safely ignore these CPU-overuse or battery-life complaints at least on
> Sandy Bridge CPUs if speex has been compiled with SSE support. I have
> directly checked the impact of the resampler choice on the battery life
> of my Sony Vaio Z23A4R laptop, under the following conditions:
>
> 1. The whole system is in initramfs. The initramfs just plays a
> CD-quality wav file with some music of ~1 minute length in a loop with
> paplay, and after each loop, logs the battery energy until less than 2%
> of energy remains in the battery. Then it saves the log to the SSD. I.e.
> there is no SSD access until the final saving of the log.
>
> 2. The screen is turned off. The hardware radio switch is also off.
>
> 3. Absolutely no keyboard/touchpad interaction.
>
> 4. Default volume, headphones connected, resampling from 44.1 to 48 kHz
> achieved by setting both default and alternate rates to 48000 Hz in
> daemon.conf.
>
> 5. laptop-mode-tools are installed, in their default configuration.
>
> 6. The kernel version is 3.17-rc5, PulseAudio is from the yesterday's
> git. Everything else is from yesterday's Gentoo amd64.
>
> All these conditions are aimed at obtaining reproducible results and
> saving as much energy as possible, so that any variations due to the
> resampler are clearly visible.
>
> The CPU is: Intel(R) Core(TM) i7-2640M CPU @ 2.80GHz (with available
> frequencies from 0.8 to 3.5 GHz).
>
> Result: with speex-float-1, the laptop lasted 26371 seconds, while with
> speex-float-5, the result was "only" 25997 seconds. I.e. less than 1.5%
> of difference (and even less under more realistic conditions, i.e. with
> the SSD, WiFi and display being on), or only 81 mW of extra power
> consumed. And I don't yet know the standard error (will repeat the test
> several times and report separately).
>
> Note: for "real" mobile devices like phones, the impact will be more
> significant. So I limit my "ignore complaints as invalid" proposal only
> to laptops with Sandy Bridge CPUs.

Thanks for the test. i7 Sandy Bridge CPUs are not my primary concern 
either (if you have an i7 CPU then you probably have a big battery to 
fuel it, too), but what about Raspberry Pi, tablets, etc. And everything 
in between.

That said, even for an i7 Sandy bridge, the question is how often will 
you be annoyed because of resampler noises, vs how often will you be 
annoyed because you've run out of battery.

As a related question, when you say that we have a worse resampler than 
"proprietary OSes", that's only desktop OSes you're comparing us to, I 
assume - not iOS, Android, etc.


-- 
David Henningsson, Canonical Ltd.
https://launchpad.net/~diwic