freq_from_AC.py

def freq_from_AC(sig, fs):
    corr = np.correlate(sig, sig, mode='full')
    corr = corr[corr.size/2:]
    
    # Find the first low point
    d = diff(corr)

    # first point with pos. 
    start = find(d > 0)

    # Find first peak after first low point
    peak = argmax(corr[start:-2]) + start
    crossings = interpolate(corr, peak)

    return fs / px