Messages in this thread | | | Date | Tue, 11 May 2010 19:10:25 +0200 | From | Daniel Mack <> | Subject | Re: [alsa-devel] USB transfer_buffer allocations on 64bit systems |
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On Tue, May 11, 2010 at 05:48:11PM +0100, Pedro Ribeiro wrote: > I'm clueless about the whole underlying process but I don't think it > is related to playing a file from the disk or another USB device. > > I don't need to play any file for this interference to be heard - I > just need to "open" the device. By this I mean that if I create a JACK
... which will stream zeros. Sure, that should also trigger the bug then.
> server or if I open the device using the ALSA backed in a program like > Mixxx I immediately start hearing the cracks and pops in the speaker. > But to answer your question, playing a file from the hard drive using > aplay I can also hear the interference - but only when the sound is > playing. As soon as the sound stops and the audio device is "closed", > no interference occurs.
Yes, because the stream is stopped, pending URBs are unlinked etc. That's completely expected.
> However, when using the JACK server, which probably opens and polls > the audio card constantly (its a low latency audio server) I don't > even need to be playing any sound for the interference to be constant.
That shouldn't affect the driver itself but just put the ALSA core under pressure.
> I can also see it since I have 4 output leds in the USB audio card and > even if I'm only using 2 channels, the 4 channel leds light up with > interference as the sound cracks and pops.
No surprise here. The 4 channels are mux'ed in an interleaved fashion, so if the buffers contain rubbish, you will hear artefacts on all channels.
Daniel
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