pops and cracks

[Jan Kokoska]

On Fri, 2004-10-15 at 12:36 +0200, Christian Casimir wrote:
> Hi,
> 
> 
> I get really annoying pops and cracks, NO MATTER what the volumes are in 
> the mixer... If I put the volume down, I just get quieter pops and 
> cracks, but it won't prevent them...
> 
> Any idea ?

1) Check your mixer settings, there should be no channel at max,
magnifying the noise. Actually I can see you do this already, so maybe
skip to the second point.

2) If your mixer settings are fine, test this with a 2.4 kernel, e.g. in
Knoppix which has both.

What magic is that? Well, process scheduling resolution default changed
from 100 Hz to 1000 Hz between 2.4 and 2.6 (somebody probably can tell
the precise versions).

If there is a "signing capacitor" on your board, which might resonate at
1 kHz (or actually somewhere else, but 1 kHz being sympathetic frequency
to that, and unlike 100 Hz, unfortunately audible) you would hear noise
every time it gets discharged/recharged. Entering power state, checking
bus, whatever circuit is it in. With 100 Hz the problem is the same,
except you wouldn't hear it (humans can still sense it at high
intensity, vibrates in your stomach, not the case with audio
reproduction unless you have some impressive stage set).

If this turns out to be the cause (and your hear nothing on 2.4), you
can recompile 2.6 after editing Hz in include/asm-i386/param.h.

HTH,

Jan