[pulseaudio-discuss] pulseaudio (V5) incorrect rate detection on usb sound card with raspberry

[Tanu Kaskinen]

On Tue, 2014-10-28 at 11:39 +0000, mailing lists wrote:
> Hello Tanu,
> 
> > I'm not sure if you mentioned this already before (sorry for not
> > bothering to check), but is the PA version the same between the
> > machines? If not, then something may have been fixed in PA, but in any
> > case it seems more likely to me that there was some change in the kernel
> > driver or alsa-lib that fixed the issue that makes PulseAudio conclude
> > that the sound card doesn't support 44100 Hz.
> 
> raspbian comes with PA 2, but I did compiled PA 5, just to discard
> this type of problems, you can see the output here and yes both test
> are with PA 5:
> 
> http://lists.freedesktop.org/archives/pulseaudio-discuss/2014-October/022015.html
> 
> I don't think there is a kernel driver or alsa-lib bug because other
> software like the Music Player Daemon haven't problem using the alsa
> device with only 10% of cpu usage (mp3 decoding), but with mpd
> Pulseaudio output or any other program (local or remote) cpu is
> 100% ... you known music is 44100 and PA detects a 48000 sound card so
> it needs resampling.
> 
> That I don't understand is how PA determines sound card capabilities.... 
> 
> any clue?

If the same PulseAudio version works on a newer kernel but not on an
older kernel, then that very strongly suggests that something was
changed in the kernel that made it work. If MPD works also on the older
kernel, then apparently PulseAudio and MPD do something differently.
Feel free to compare the source code of MPD and PulseAudio to see if
PulseAudio does something wrong (I lack the motivation to do that
myself). The "Device %s doesn't support %u Hz, changed to %u Hz."
message is printed from src/modules/alsa/alsa-util.c, so that's a good
place to start.

-- 
Tanu