Hi! I had a similar problem in my laptop when using a USB soundcard (Edirol UA-25). For me it was not necessarily associated with xruns.
Since ardour doesn't record the noise, I would say that the problem is not in jack, but in the alsa driver. It sounded also more like a distortion than noise, since when the output levels were low the effect was less noticeable. I found empirically that harddisk writing operations like saving a file in an application would sometimes make the distortion stop, I'll be damned if I know why (interrupts?). Anyway, setting my USB unit to work at 48 kHz made this problem practically disappear. HTH, Luis > it happens randomly, while I play a soft synth, that jack XRUNs once, > and the audio become crappy, noisy, like a kinda of digital > effect....bit crusher? > > then all synthesizers (all audio apps) sound the same sh*t... > i tried recording with ardour the output, and the output is clean, so I > guess is a problem of sync or something that has to do with the hardware > (soundcard). > > in order to record this noise, i had to connect the soundcard output in > its input and record it via analog in: > http://xaero.ath.cx/jackbug_stereo.wav.bz2 (it is a stereo file, with > the clean track panned on the left, and the dirty one on the right). > > i hope it could be useful to debug the problem... > what other information I can provide useful for debug? > note that this happens with many version of alsa (1.0.9b, 1.0.10rc2, > 1.0.7 or less) and with many kernels (gentoo-sources (slightly patched > for speed improvement), ck-sources, ck-sources+realtime-lsm) > > i hope to solve this problem, since my audio desktop is unusable as si, > since audio crasher after playng for just 5 minutes :( > >
