[PlanetCCRMA] Sound (is it sound if you cant hear it?) above 22kHz

Spec specialaka@blueyonder.co.uk
Tue Mar 1 14:23:02 2005

Hello All, just loaded CCRMA (top work all the various package 
writers/modders) and am stunned by how good Linux is now at audio, 
anyway some first experiences with 96kHz sampling.

was playing with Jack / jaaa and my audiophile 2496 card, was amazed to 
see when I put it in
96kHz sampling mode how much sound/inaudible? noise there is at 23kHz 
and above.

1. The onboard sound card via chip has vey high noise (-50db by jaaa), 
and consequently there is a lot of noise at several peaks above 23kHz 
and below 48kHz  (seems to be common computer self noise which can be 
seen on both sound chips/cards at diff levels)

2. the audiophile much lower noise level -(-110db by jaaa), but can 
still see the computer self noise signature albeit at a much lower 
physical level (about 4-8 quite loud/powerful peaks above 23kHz that 
fluctuate in amplitude periodically)

3. capturing the stereo out of a roland low end keyboard shows a lot of 
activity above 23kHz almost as much power as below 23kHz.  Was suprised 
by this. but tested and retested and it appears to be a fact.

4. pretty sure my signal path is clear coming thru mixer, as recording 
guitar and voice thru mic on audiophile 96kHz shows very little activity 
above 23kHz (except on voice noise sounds also very different pattern 
from the computer self noise)

5. when I put the mic near the computer, I can actually record audibly 
the self noise I see on just the sound card. (same peak pattern 
throbbing at roughly same freqs) (wow the mic (sure sm) has quite a 
response above 22kHz)

I have been having some problems anyway with an audibly loud and very 
annoying approx 7900kHz freq from 2 of my (quite expensive darnit) power 
supplies, but only when I connect either or both of my 2xseagate 
barracuda  7200rpm hard drives.  The PSU is quiet when the drives are 
not connected.  (Yes it is the PSU making the noise, I cant understand 
it, is it 12v being over-used or feedback or something)

currently running on a very cheap psu which has got rid of the audible 
(7.9kHz) noise???, but I have just spotted this inaudible signature

I have yet to put the other PSU's back in and see what the computer self 
noise is with
each of them.  But I cant stand the 7900 whine with them so somethings 
got to change...

Anyone got any suggestions on best PSU's/cases/case mods and eliminating 
sound card/computer self noise (even above 23kHz).