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
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