Audio Problem with MPEG-1 Files: Inherent and standard? Or my card or computer?

[Ken Reeser]

I have recently discovered an audio artifact in mpeg-1 encoding that I am surprised to have never noticed before, and I'd like some opinions and possible solutions.

Background: This pertains to MPEG-1 encoding, and the audio specifically. Yes, I know that other formats are "better", but this is the format I need to use.

I have noticed a faint hum or whine in all my MPEG-1 files, whether created on my MG100 card or my Broadway card. I have done about 500 tests with various sources, and the hum is always there, although to a greater or lesser degree, depending on the volume level of the source. I can hear the noise as soon as I activate the software and plug in a video source. I have uploaded some test files to listen to, if you're interested.

http://members.dslextreme.com/users/...grip/Lit01.mpg
http://members.dslextreme.com/users/quoth/X100.01.mpg

After exhaustive testing and reconfiguring, I decided to look for other sample videos on the web, and discovered these posted on Broadway's own website:

http://www.datatranslation.com/conte...kiDemoHigh.mpg
http://www.datatranslation.com/conte...ngDemoHigh.mpg

You'll notice that the same hum is present at the beginning and end of these videos as well, when the music is down and there's a brief moment of silence. I believe they are deliberately using music throughout to mask the noise!

So my questions are:

1. Is this low-level noise inherent in all MPEG-1's?
2. Is there something I can do to minimize the noise when encoding? Is there some sort of grounding, shielding or whatever that will eliminate it?
3. Has anyone else noticed this audio problem and dealt with it?

I know that room noise and music will mask the sound, but not everything I encode will have these options, and that's not really the point. I want noise-free audio. I am considering an Optibase card as my next encoder, especially if it doesn't make this noise. Doeas anyone have any experience with these?