12 Nov
2006
12 Nov
'06
4:30 p.m.
A while ago I had a very similar problem, on an Athlon
XP desktop machine.
Whenever I ran jack at low latency, there was a high pitched noise coming
from somewhere inside the case. I was unable to pinpoint where exactly it
came from, but I'm pretty sure it originated somewhere on the mainboard,
maybe the CPU or the PCI cards.
But it didn't just come from the case, it was also audible on headphones,
on both my PCI sound cards!
This is EXACTLY the problem I faced, and EXACTLY the response I had to
it. Where the hell is that faint hum coming from?
What was especially confusing is that it was audible both without
headphones, very slightly, and with headphones, amplified.
At 256 frames/second, the noise was barely audible...
At 128 it was quite
easily noticable, and at 64 it became downright annoying. At 32 or 16
frames/second it was even worse...
This is exactly the behavior I experienced. Very slight at higher
latencies; however, I tried it at my friend's club and over the
high-powered amps it is still a clear annoyance, not to mention not
being able to sing and run effects over it at low latency.
But the most intriguing part of the whole story: Not
only did the noise
get louder at a lower latency, it also seemed to precisely double its
frequency when running at halve the number of frames. I even tried to
measure the frequency of the noise. As far as I remember, when running
jack for instance at 44100Hz, periodsize 32, the noise was at exactly
44100/32 = 1378Hz!
That is absolutely fascinating. I WILL investigate this; if it
coincides, we have a VERY strong case that this is the same problem.
Anyway, this whole issue went away after I disabled
athcool (a utility to
reduce heat and power consumption on Athlon CPUs) while running jack. But
still all of this remains a mystery to me...
What would be the corresponding utility for a Pentium 4 mobile (used
before centrinos, slightly modified for notebook assemblage but still a
full Pentium 4) be? How could I completely de-activate power management
and open the case and put some ice cubes in? (IE manage power myself,
with a room fan, or liquid cooling, or whatever...)
Carlo