Audacity Forum

I have been joining together a radio story that was broadcast in short extracts. These are on audio tape and I have copied them into Audacity beta.

One recording seems to have been broadcast with a single tone for part of it's length. The trouble is the volume of the tone rises and falls with speech parts so that if I use Noise Removal to cut it from the 'silent' sections it is still left in the speech, but with the added irritation that it then turns on and off with each burst of speech because it has been removed in between.

Is there any way to identify just this tone and remove it at whatever amplitude it happens to rise to, or do I just have to get used to this background artefact of my old recording?

Cheers,

S

If it is just "one" frequency, then it could be easily removed with a notch filter, however a "tone" may be made up of very many frequencies and that can make it difficult or even impossible to remove satisfactorily.
Could you upload a couple of seconds of the problem recording (in WAV or FLAC format).
There is an "Upload" tab below the compose message box - WAV files must be short (1 or 2 megabyte size limit)

Thanks very much Steve - it sounds like one tone to me but when I zoom in on it all I seem to see is a row of little tick marks that look like a measuring scale.

(The uploader says there is a 1 meg limit by the way: hope that is enough.)

Cheers,

S

You may win. It's very low and it does appear to be a single tone. 1753 or 1771 depending on which instrument you believe. Notch filter each one and see if it goes away.

http://audacityteam.org/download/nyquistplugins
About 2/3 of the way down.

Koz

I've never used this filter, but if it has an amplitude or depth control, set it for the minimum needed to suppress the tone and avoid damaging the show. For example, if it's already -40 or so, another 20 will take it to 60 which is just about inaudible.

You can also try the noise removal tool and let it design the filter for you. Again, apply just enough and no more.

Koz

It has a width (Q) and a frequency control.
I've not listened to the sample yet, but going on what Koz has said, try the frequency set to about 17560 and the Q set to 2.
Also try it at 1753 and at 1771. Pick the best of the three.

I'm pleased to say this is almost the perfect show for these tools. The tone is very low already and would vanish with a little gentle, graceful help.

Contrast that with a more normal poster trying to dig a voice out of much louder audio garbage. You are sweetening an audio track. They are creating a track out of trash.

Koz

Excellent suggestions everyone thankyou!

The tone is just about removed by all these frequencies!

What was it that you all used to measure the frequency so accurately - by ear it was twice as high as I thought it was?

It is very impressive how keen and knowledgeable you are on all this.

I still have a little trouble getting the voices to sound right after noise reduction in stereo, but in mono it is now all working well.

Thanks very much,

S

The tone center is 1771. I'd love to say I'm just really good that way, but in fact I used the analyzer.

Select some of that noise-only, voice-free segment after "Giddy."

Analyze > Plot Spectrum.

Size 8192, Log Frequency, Pull the display as large as you can.

Move the cursor close to that one lonely spike on the right. Read the peak value.

There goes my secret.

<<<I still have a little trouble getting the voices to sound right after noise reduction in stereo>>>

That's where the danger comes. You need to do "noise reduction" without affecting the show at all. It's really easy to overdo it and trash the show. The tools are carefully tuned violins, not military artillery.

Koz

I did look at the spectrum tool, but couldn't quite see what to do with it once I had analysed. I was probably choosing too wide a clip.

Anyway, thanks, and this is all very informative.

Cheers,

S