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    SubjectRe: [alsa-devel] USB transfer_buffer allocations on 64bit systems
    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

    > 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

    > 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


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