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I have a sample waveform of an air conditioner and want to see if any low frequencies (10 Hz which is harmful to human health) exist in the wave.  How can I do that?

Granted the frequencies picked up in the recorded file depend on the quality of the recording and the recorder and lower frequencies may not have been picked up. 

I've looked at

The quantity ω(x):= limsup_T->+infinity Pi/T*ν(x,T) is said to be the frequency of a function x:[0,infinity)->R,
where ν(x,T) equals the number of zeros (taking into account  the multiplicities) of the function x on the interval [0,T].
a) To estimate from above the frequency of any non-zero solution of the ODE diff(x(t),t$2011)+x(t)=0.
b) To find the frequency of the function x(t):=sin(t)+sin(Pi*t).

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