Simple Voice Activity Detection based on Long-term Spectral Divergence

ltsd_vad.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import wave
import numpy as np
import scipy as sp
import matplotlib
    
WINSIZE=1024
ORDER=5
sound='howl6t1.wav'

def read_signal(filename, winsize):
    wf=wave.open(filename,'rb')
    n=wf.getnframes()
    str=wf.readframes(n)
    params = ((wf.getnchannels(), wf.getsampwidth(),
               wf.getframerate(), wf.getnframes(),
               wf.getcomptype(), wf.getcompname()))
    siglen=((int )(len(str)/2/winsize) + 1) * winsize
    signal=sp.zeros(siglen, sp.int16)
    signal[0:len(str)/2] = sp.fromstring(str,sp.int16)
    return [signal, params]

def get_frame(signal, winsize, no):
    shift=winsize/2
    start=no*shift
    end = start+winsize
    return signal[start:end]

class LTSD():
    def __init__(self,winsize,window,order):
        self.winsize = winsize
        self.window = window
        self.order = order
        self.amplitude = {}

    def get_amplitude(self,signal,l):
        if self.amplitude.has_key(l):
            return self.amplitude[l]
        else:
            amp = sp.absolute(sp.fft(get_frame(signal, self.winsize,l) * self.window))
            self.amplitude[l] = amp
            return amp

    def compute_noise_avg_spectrum(self,nsignal):
        windownum = len(nsignal)/(self.winsize/2) - 1
        avgamp = np.zeros(self.winsize)
        for l in xrange(windownum):
            avgamp += sp.absolute(sp.fft(get_frame(nsignal, self.winsize,l) * self.window))
        return avgamp/float(windownum)
    
    def compute(self,signal):
        self.windownum = len(signal)/(self.winsize/2) - 1
        ltsds = np.zeros(self.windownum)
        #Calculate the average noise spectrum amplitude based　on 20 frames in the head parts of input signal.
        self.avgnoise = self.compute_noise_avg_spectrum(signal[0:self.winsize*20])**2
        for l in xrange(self.windownum):
            ltsds[l] = self.ltsd(signal,l,self.order)
        return ltsds

    def ltse(self,signal,l,order):
        maxamp = np.zeros(self.winsize)
        for idx in range(l-order,l+order+1):
            amp = self.get_amplitude(signal,idx)
            maxamp = np.maximum(maxamp,amp)
        return maxamp

    def ltsd(self,signal,l,order):
        if l < order or l+order >= self.windownum:
            return 0
        return 10.0*np.log10(np.sum(self.ltse(signal,l,order)**2/self.avgnoise)/float(len(self.avgnoise)))
 

if __name__=="__main__":
    import matplotlib.pyplot as plt
    signal, params = read_signal(sound,WINSIZE)
    fig = plt.figure()
    a1 = fig.add_subplot(111)
    a1.plot(signal)
    
    window = sp.hanning(WINSIZE)
    ltsd = LTSD(WINSIZE,window,ORDER)
    res =  ltsd.compute(signal)
    fig = plt.figure()
    ax = fig.add_subplot(111)
    ax.plot(res)
    plt.show()