Chris@3: 
Chris@3: import numpy as np
Chris@3: 
Chris@3: def rms(samples):
Chris@3:     """Return the root mean square of the given samples"""
Chris@3:     return np.sqrt(np.mean(np.array(samples)**2))
Chris@3: 
Chris@3: def autocorrelation(samples):
Chris@3:     """Return the autocorrelation of the given samples, as an array with zero lag at the start"""
Chris@3:     acf = np.correlate(samples, samples, mode='full')
Chris@3:     return acf[len(acf)/2:]
Chris@3: 
Chris@3: def bpm_to_lag(bpm, hops_per_sec):
Chris@3:     """Return the autocorrelation lag corresponding to the duration of a beat at the given tempo in bpm"""
Chris@3:     return int((60.0 / bpm) * hops_per_sec)
Chris@3: 
Chris@3: def lag_to_bpm(lag, hops_per_sec):
Chris@3:     """Return the tempo in bpm whose beat duration corresponds to the given autocorrelation lag"""
Chris@3:     return (60.0 * hops_per_sec) / lag
Chris@3: