[mythtv-users] Audio - hiss (Buzz)

Scott Croft scott.croft at cox.net
Wed Mar 15 02:05:12 UTC 2006


On Mar 12, 2006, at 8:01 PM, Scott Croft wrote:

> 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
> input.
>

Are you saying that you have hum *until* you plug the patch cord into
the the line in ?

Is this hum what you initially described as "hiss"?

Everything else you say is more or less normal, touching the "hot"
input wire will normally cause hum, your body is acting as an antenna
and picking up the ambient 60-cycle buzz in the atmosphere around
you. Shorting the input to the case (ground) will normally eliminate
most if not all output.

What you are proving is that your audio amplifier seems to be working
more or less normally, but if you have hum with nothing connected to
the input which goes away when you connect a cable to the line in I
would look for a bad input connector (loose/cold solder joint etc.)

I also note that you initially said you had PCM turned up and line in
down ?? For the setup you describe this would be wrong, you would
want PCM down or muted and line in turned up, the TV card in your
case is no different from the iPod as a sound source.



Yes it is more of a Buzz/hum and not a hiss, I guess I did not use the right
audio term!

The hum is not present at all until one of two things happen.  I
short/ground the left or right channel going to the line in, or I plug the
sound card line in to the TV card line out with the patch cable.  After
reading and asking question I agree with you that when I touch or ground the
line in I should here the buzz.  The problem is that I get the same results
when I connect the TV card to the line in on the onboard audio (also get the
TV audio).  Both left and right channels have the buzz.

I think that I tried the mixer settings you describe (think I read something
to the same effect) and could not get any sound at all with settings like
that.  Not sure about this.

Since my last mail I have added a PCI sound card and disabled the onboard
audio in the bios.  This works with no trouble.  Not the solution I wanted,
but it works.  I am using all the same settings and hardware with the
exception of the onboard audio.  I guess this tells me that my brand new
onboard audio is broken, or I have some type of grounding problem with the
PC??

Again thanks for the input, it is much appreciated.  I am moving on to get
the remote control working, and the s-video output to fill my entire TV
screen.

Scott





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