On Sat, 13.10.07 00:15, Seth Forshee (seth.forshee at gmail.com) wrote: > > Hi Lennart, > > On Sat, Oct 13, 2007 at 01:05:16AM +0200, Lennart Poettering wrote: > > > 1) Resampling. PA uses libsamplerate, which uses a lot of > > > floating-point math. There was some discussion about a fixed-point > > > resampling library a while back (I think it came from the Speex > > > project), but I haven't seen anything about it in a while. > > > > The code has been available in the "lennart" branch in SVN for a > > while. Just pass --resample-method=speex-float-0 or similar. > > Cool, that's good to hear. Of course, this should read --resample-method=speex-fixed-0, sorry for the confusion. > > > 2) Volume scaling. PA converts its internal, dB-based volume level into > > > a floating-point linear scale that is applied to each sample of a > > > stream. The code that does this for a single stream is reasonably > > > sane (although I would argue that the internal volume representation > > > should be the linear version instead of the dB version so that it > > > would only need to be converted when the volume is set), but the code > > > for scaling multiple streams is horrendously inefficient. I did a > > > quick rewrite of this code that took CPU utilization on a P4 class PC > > > from over 30% to under 10% when playing multiple streams (I don't > > > remember exactly how many, probably 2-3). I never cleaned up the > > > code enough to bother with submitting a patch though. > > > > Hmm, the current code translates the volume spec first, and only > > after that runs the inner loop. Should be OK. It's not liboil > > accelerated, but should be good enough. > > > > http://pulseaudio.org/browser/branches/lennart/src/pulsecore/sample-util.c#L344 > > Yes, this code looks fairly good at first glance. But I was actually > referring to another section of code. It's the volume scaling in > pa_mix() for per-stream volumes that I found to be extremely slow. Indeed, the code sucks. I'll fix that. Thanks for the pointer. Lennart -- Lennart Poettering Red Hat, Inc. lennart [at] poettering [dot] net ICQ# 11060553 http://0pointer.net/lennart/ GnuPG 0x1A015CC4
