[mythtv-users] Audio - hiss

Scott Croft scott.croft at cox.net
Mon Mar 13 03:01:21 UTC 2006

Further to my post below I have found some additional information.  It would
seem to be a "grounding" type issue I think.  When I plug the patch wire
into the line in of the sound card there is no hum.  If I pinch the free end
of the patch wire with my fingers I can cause the hum.  I then attached an
old headphone jack to the line in in the onboard audio card.  With the wires
exposed I experimented with the audio in.  If I ground the center audio wire
with my fingers or something other than the CPU case I can create the
hum/hiss in the right or left channel.  Grounding the wire to the CPU case
dose not seem to cause the hum.  Grounding the "ground" wire from the left
or right wire dose not seem to cause a change in the hum.  I am not much
good with audio so anyone have any suggestions?  Thanks in advance for any


First many thanks for the feedback.

I do not have much that can be moved around in the case.  It is a brand new
home built PC and only has two cards in it.  The AGP video card can not
move, and the TV card I have moved from the first to last slot and several
of the five other slots.  I have a DVD drive and one hard drive installed.
I tried some quick tinfoil shields, moving cables, checking for lose
connections, etc.  I do not have an analog cable running from the DVD to the
MB CD input.  During all my messing around I listen to the hiss with
headphones to see if I can tell any difference.  So far nothing I do can
change the hiss in the least bit other than changing the volume of the
system.  The hiss will go away if the line from the TV card to the sound
card is removed, or for a second when switching channels.  My undedicated
guess is one of two things.  I still have some type of feedback loop (bad
mixer settings or volume levels), or some type of grounding or short between
the TV card and the sound on the mother board.  I will try "borrowing" a
sound card from another PC to test the outcome tomorrow.

I could use some luck because I do not seem to have skill!

-----Original Message-----
From: mythtv-users-bounces at mythtv.org
[mailto:mythtv-users-bounces at mythtv.org]On Behalf Of Brian Wood
Sent: Friday, March 10, 2006 10:19 PM
To: Discussion about mythtv
Subject: Re: [mythtv-users] Audio - hiss

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

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.
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