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

David dplist at free.fr
Sun Nov 2 10:20:39 EST 2003

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

- 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 !


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