[linux-audio-user] noisy capture->playback

Hello all ! What could I do about the following problem ? I have an M-audio delta66 + omni I/O (preamp/breakout box). This card has an onboard digital mixer that allows hardware monitoring of inputs. - when setting this mixer to directly route a HW input to a PCM output, the sound is perfectly fine. The signal goes through both an A/D and a D/A conversion before reaching my ears. I suppose that if I had a ground loop problem (or other analog noise source), I would hear it with such a setup. - now, when using jackd to route (with no jack client in between) the alsa capture port associated with the HW input to a playback port, the sound is full of horrible "blips". I use : - IRQ #10 for the delta66 (I even disabled the USB controller of the motherboard which used IRQ#11, with no better results). - a patched for LL 2.4.19 kernel, ext2 filesystems and hdparm'ed HDs. - alsa 0.9.6 - a tmpfs work directory for jackd that I start with '-R' as root. How could I isolate the source of this very annoying problem ? Is there a way to route an input to an output through ALSA only without using jackd (and the hw mixer too of course) ? Maybe that would help tracking down the culprit ... I'd appreciate any hint on this. Thanks a lot ! -- David