[mythtv-users] Audio - hiss

[Brian Wood]

On Mar 10, 2006, at 8:42 PM, Scott Croft wrote:

> I have come to the end of all I can think of to fix the high  
> pitched hiss in
> the audio of my real time or playback of myth TV.  I am using an old
> Hauppauge WinTV card and have the audio out jack on the TV card ran  
> back
> into the line in of my on board Nvidia audio card.  Have set and  
> tried all
> the combinations I can think of in the alsamixer control.  I  
> currently have
> all settings muted and turned down with the exception of Master 70%/ 
> on, PCM
> 70%/on, LineIn 0%/muted, Capture 0%.  I can listen to the audio out  
> jack on
> the TV card with headphones and the sound is fine.  I can feed an  
> Ipod audio
> into the loop cable plugged into the onboard audio line-in and it  
> works fine
> with myth into my TV with no hiss.  I have added a "magnet filter"  
> to the
> audio patch line to try to eliminate the noise with no change.  I have
> switched the power to the PC to another circuit in the house.  Have  
> moved
> the TV card to another PCI slot, and replaced the TV card with an  
> extra
> identical one.  Nothing seems to work.  The hiss "volume" seems to  
> follow
> any of the volume controls up and down.  Any help or suggestions  
> would be
> greatly appreciated.
>

There is a lot of "hash" floating around in a PC case, it sounds like  
some of this is getting into your sound system.

The fact that it goes up and down in level  would seem to confirm this.

You can try things like re-routing cables, moving cards around if you  
can, trying to get as many of them as you can as far away form the  
sound card/ built-in audio chip.

If you have an analog cable going from your CD drive to the card/ 
board you could try removing it (even if this input is muted crap can  
get in).

Getting more aggressive you could try shielding the audio components  
in some way, but be very careful if you use aluminum foil or anything  
like that, you don't want to short any electrical components out.

You could put termination resistors across unused analog inputs, or  
even try dead shorts.

If the frequency is high enough, by pass capacitors might help.

Replace/tighten any screws in your case, if you have removed any case  
parts (panels etc.) try replacing them.

Make sure the screws securing your motherboard are tight, and that  
none are missing.

If your audio is integrated, you could try going to an add-on sound  
card, this is one of the more common complaints about integrated sound.

If you have optical output capability try using it instead of  
electrical.

Sacrifice a goat, but be sure to be facing Redmond while doing so.

Basically, you want to "change things around" and see what helps and  
what doesn't. This is sometimes more art than science.

Good luck.