Cycle measurements

I would like to count the number of cycles of the complete audio track or part of it.
How is this possible ?

If you have a pure sine wave or other single-frequency signal you can simply calculate it from the frequency and time. If you don’t know the frequency, use Analyze → Plot Spectrum, although that’s not accurate enough to get the exact number of cycles.

In case you don’t already know this, frequency (Hz) is cycles-per-second so 1 second of 1kHz audio is 1000 cycles and one minute is 60,000 cycles, etc. Regular program material contains many different simultaneous and constantly-changing frequencies (which you can see with Plot Spectrum).

For more complex waveforms and/or for a more-exact calculation you can find the zero-crossings and divide by two. I assume [u]Nyquist[/u] can do that, or Matlab (and there are free “Matlab clones”) can do all kinds of math & analysis with audio files.

If it’s a mixed audio track such as music, it’s not possible.

If you’re measuring a tone, you can use Analyze > Plot Spectrum and increase the size setting up to a high value. Pull the window very wide to make the spike easier to see. Center your cursor over the spike and read the frequency.

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400Hz or cycles per second in this case. This tool will read multiple tones together, but music or real-life sounds have too many tones to accurately measure.

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You can also change the timeline to View > Spectrogram with the drop-down menu on the left, but that’s not very accurate.

Fair warning that Plot Spectrum needs a certain duration of the tone to measure properly, so brief tones can be difficult to measure.

This technique can be handy if you think you have wall power problems. Those have a signature. Spikes at multiples of 60 in the US and 50 in the UK.


As DVDdoug above, if you need an exact measurement, you need the Zoom tools and very strong coffee.

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There is a caution here. Scientists and Audacity don’t always get along very well. If there is ever a choice between strict scientific accuracy and sounding good, Audacity will almost always opt for sounding good.


Additional caution. All this is only as accurate as your computer sound system or other audio devices. It’s not unusual for someone to record very high quality separate sound for a home video and find that the duration of the video and the duration of the sound track don’t match because of digitizing accuracy issues. The movie people have stupid-expensive sound recorders to get around this.