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Old Jan 24, 2013, 09:35 AM
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United States, NJ, Edgewater
Joined Feb 2012
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Measuring motor RPM from recorded motor sound using free software

Iím looking for a way to measure the RPM of my motor by analyzing the sound file. By measuring the RPM and the voltage drop we can intern calculated the KV of the motor. I did find this old post that has some good information but would like to use open source software that is not system dependent so that anyone can use it. Audacity seems to fit these requirements and runs on Macs, Windows and Linux.

So far I have the motor sound recorded and the sound sample imported into Audacity as a WAV file. Can someone provide clear directions and a technical explanation on how to measure the RPM from here ? I guess this would requires some noise filtering and maybe some signal transforms ?

I thing the overall process would be :
1. from the recording, isolate a clean sample of the sound to analyze which can be done from visual inspection of the WAV file
2. run a filter to remove noise (Low pass filter or an amplitude filter??)
3. run some type of transform to easily identify the prop frequency (spectrum plot ?? )
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