On 11 May 2010 18:10, Daniel Mack <daniel@xxxxxxxx> wrote: > 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 > > So what would be the testcase you would like me to try? Pedro -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
