Fernando Lopez-Lezcano wrote:
On Sat, 2006-11-11 at 13:51 +0100, Daniel Wagner wrote:
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!
Is an interrupt fired at each period? If so the cpu will use more power
(or woken if it was asleep); a small power 'surge' which can of course
have an influence on any analog hardware near by.
Really sounds like the power supply, the high frequency transformers can
"sing" with changes in load if the windings are a bit loose. I think
capacitors can also do that.
Somebody I know had a fanless computer in his room (a very old machine
that really did not need fans if the case was left wide open) and the
only remaining sound was some component singing with the network
traffic...
A simple test to see if the load is causing the hum:
Open a PDF in acroread (if you have it installed). I noticed that I can
make some computer sing by dragging the view (hand tool) in acrobat
reader. acroread seems to contignously redraw when you use the hand tool.
The solution: get a high quality power supply & possibly a high quality
mainboard too. But as you are experiencing this with a laptop there's
not much you can do.
Pieter
PS: Maybe this is the one good reason to choose Apple over Dell... ?
