Detecting & Locating a Tone

I’ve looked for but not found any way to scan through a sound file to detect and locate (for example move the cursor to) a brief constant frequency tone present in the file. I have been working with the Beta version of 1.3.13, just downloaded 2.0 and have not installed it yet. Nevertheless I see no mention of the subject in the release notes, new features, FAQs, add-ons nor manual. Seems like a pretty rudimentary feature. Hard to believe there is no way to do it.


This shows a “spectrogram” view of some music with a pure tone in the middle (the horizontal line is the pure tone).

I don’t understand. Where is the time line showing when the tone began and ended? Please elaborate.



In what versions of Audacity does that tool exist? I don’t see it in 1.3.13 Beta. I downloaded but did not install 2.0 yet.

Over what duration of recording will it work? For example spectral analysis seems to be limited to 131 seconds.

If I understand your example, during the interval when tone is present there are no other signals. But I want to detect a tone that’s accompanied by voice. That’s a trivial task for a hardware tone detector. I don’t understand how I would recognize a steady tone accompanied by voice or music of equal or greater level from the graphical display in your examples. Maybe it will make sense when I find the tool on the tool bar and try it on an actual file but it doesn’t at this moment.

Click on the Track Drop-down Menu and select Spectrogram view.

– Bill

Thanks. Tried it and I see how it works now. Pretty cool!

However I’m not sure whether a Call Waiting Tone that occurs in the midst of a telephone conversation while two people are speaking will be visible, and it’s very time consuming to scan through an hour long telephone conversation recording looking for the Call Waiting Tone visually.

I doubt that it will be easily visible.
Do you know what the tone frequency is? 440 Hz?
How loud is the tone? (if recorded when there is no voice, how high is the waveform compared to the normal voice level?)
It may be possible to write a plug-in to detect a tone if the exact frequency is known, provided that the tone is not too quiet.

Here’s a new experimental plug-in that you can try.
Try it on a short selection that contains a beep first so that you have an idea of the necessary threshold level.
The default tone frequency is 440 Hz.

Note that this is an experimental plug-in. Ensure that your work is backed up before trying this plug-in.

To install, download the attached file and place it in your Audacity plug-ins folder then restart Audacity.
The plug-in is called “Tone Finder” and it will appear in the Analyze menu.
ToneFinder.ny (1.46 KB)

Thanks. I will try it and let you know the results.

Yes, 440Hz is the standard Call Waiting Tone for North America. The published specification is -13dBm for 300 mS. Whereas earlier analog electronic switching systems interrupted the speech channel to the distant party during application of CWT, digital systems do not. So the tone is quite unobtrusive to the called party.