high pitched background noise

[dhanson10191]

I'm trying to make an audio recording of a presentation on windows 7.

The recording quality is excellent for my voice, but I can't figure out how to get rid of a constant high pitched squeaking sound. I'm using a mic... but this sound is there whether I record something or just leave it silent. Do you have any suggestions on how I can set audacity up so all I hear on the recording is my voice?

David
[email protected]
715-770-9747

[steve]

This is a guessing game at the moment.
Laptop computers have a habit of producing a high pitched whistle due to interference from the power supply. The most simple "cure" is to run the laptop on batteries.

If that's not it, could you give details of what equipment you are using, how it is set up and what you are doing (step by step).

[Trebor]

Clock noise ? , which can be removed by notching ...

Before-after whistle artifact removed.wav

(390.28 KiB) Downloaded 1654 times

If it is clock artifact then a spectrum of a "silent" bit will have spikes at reqular intervals ...

clock noise and harmonics.png (19.62 KiB) Viewed 29421 times

The spikes can be removed with a notch filter ...

Notch filter#2 plugin for Audacity,( NY in ZIP).zip

(628 Bytes) Downloaded 1516 times

BTW for some reason notching does a better job at curing this problem than Audacity's noise reduction.

[dhanson10191]

I think the problem was with my mic. When I unplugged it and just recorded straight to the computer, there was no background noise... however... sound quality was not nearly as good. Is there a recommended mic that is commonly available? I don't know what to tell you about "step by step" other than I open the software, press record, and play back with the high pitched background. It doesn't seem to matter how many hertz, or bits. Thanks for your prompt reply!

[Trebor]

I think the problem was with my mic. When I unplugged it and just recorded straight to the computer, there was no background noise...

Possibly external mic is picking up mains hum, although that's more of a buzz than a high pitched whistle ...
http://en.wikipedia.org/wiki/Mains_hum#Tone

Possibly feedback squeal (that's usually high pitched) ...
http://www.freesound.org/samplesViewSingle.php?id=49282

You can attach a few seconds of the affected audio to your posts here, provided the file size is less than 1Mb,
we might be able to diagnose the problem from your audio sample.

[dhanson10191]

hi.wav

background trouble

(457.04 KiB) Downloaded 2638 times

here's the attachment sample

[steve]

Oh dear, there is something seriously wrong there. My first thought is that your sound card is faulty.

What sort of microphone/sound card/computer/operating system are you using? (model numbers are useful)

[Trebor]

The boiling kettle whistle is removable with the notch filter I posted above ...

'hi' before-after notched @ 4600Hz and HighPass above 25Hz.wav

(480.77 KiB) Downloaded 1063 times

But there is something fundamentally wrong with your recording
the 0.07second pulses every half second and the effect which follows half a second after you speak suggest to me that an AGC/compressor may be the cause.

It may be possible to turn off this AGC/compressor via software (unchecking a tick box) and alter the gain (sensitivity level ) manually via an on-screen slider.

These controls may be under "Microphone enhancements" in "microphone properties"...

Microphone properties-Vista.png (30.13 KiB) Viewed 29378 times

[whomper]

But there is something fundamentally wrong with your recording
the 0.07second pulses every half second and the effect which follows half a second after you speak suggest to me that an AGC/compressor may be the cause.

Microphone properties-Vista.png

hmmm.....

could there be skype or other software lurking that is causing the problem ?

[dhanson10191]

I tried everything that was posted, and nothing has worked so far... can't find AGC compressor to check/uncheck but I did spend a lot of time browsing in microphone settings. I have a Toshiba Satellite A505-S6980 with Windows 7. Intel core 2 Duo T6600. I do have skype installed on my computer, with video/voice calling. If that is the problem, how do I turn it off?