What's that loud hum & hiss?

[diefsound]

I've been using Audacity for years with no problems, but recently,
when I began recording, there arose a loud pulsing hum and hiss...
almost sounds like a ray gun fropm a 50's movie.

btw, this happens with no audio inputted at all.

What might be causing this and how do I stop it?
I'm now dead in the water.

Many thanks.

[steve]

You may have some sort of feedback going on.
If you are using Windows, check the Windows Mixer (loudspeaker icon near the clock) there is probably something un-muted that should be muted.

[kozikowski]

That's one of the down sides of being able to easily record internet shows. Doing that involves the computer feeding back on itself (play and record at the same time) and that can be dangerous. See Fiddle. Vista makes that much harder to do and Macs have never been able to do that without extra software.

Koz

[diefsound]

Thanks, koz and steve.

I've muted "SW Synth", "CD Player" and "Line In" but the noise remains.
(They were never muted before.)

Other ideas?...

[kozikowski]

You didn't correct us when we said you were on a Windows machine. Should you have?

Pull all the cables from the sound card. Line cables, speakers, everything. Restart the machine, launch Audacity fresh and click once inside the red record meters. They will come alive in testing mode and allow you to measure things without actually going into record and wasting disk space.

Do you get a reading? If the left side printing on the meters is in the -60 range, you might be able to measure sound card noise down there, but certainly not above that.

I'll jump ahead here and assume you do get a significant reading.

Open up the Windows sound control panels and start turning everything off. I'm particularly interested in items called "Mix Out" and "What You Hear." Keep closing things and [OK]. If you make it through all the available panels and you still have noise, you may have a sound card going into the toilet.

Notes:

--If you're on Vista, some of the rules change.

--The desperation move is to shut everything down, pull out and reseat the sound card (This is when you tell us you're on a laptop).

Koz