On 2014-09-30 09:04, David Henningsson wrote: > 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. I did a quick test here. I have an old laptop that runs Ubuntu 12.04, with default installed PulseAudio 1.1. Its processor is Intel Pentium M @ 1.4 GHz [1], single core, with an AC'97 codec. Running speaker-test will automatically cause resampling from 48 kHz down to 44.1 kHz, as verified with "pactl list sink-inputs". Under speex-float-1, PulseAudio consumes about 4.3% CPU. With speex-float-3, PA consumes ~8% CPU. With speex-float-5, PA consumes ~13% CPU. -- David Henningsson, Canonical Ltd. https://launchpad.net/~diwic [1] I think it's this one: http://ark.intel.com/products/27575
