def STFT(x, wlen, h, nfft, fs):
########################################################
# Short-Time Fourier Transform %
# with MATLAB Implementation %
# For Python %
# Copier: Nelson Yalta 11/03/15 %
########################################################
# function: [stft, f, t] = stft(x, wlen, h, nfft, fs)
# x - signal in the time domain
# wlen - length of the hamming window
# h - hop size
# nfft - number of FFT points
# fs - sampling frequency, Hz
# f - frequency vector, Hz
# t - time vector, s
# stft - STFT matrix (only unique points, time across columns, freq across rows)
# represent x as column-vector if it is not
if (len(x.shape) > 1) and (x.shape[1] > 1):
x = x.transpose()
# length of the signal
xlen = x.shape[0]
# form a periodic hamming window
win = hamming(wlen, False)
# form the stft matrix
rown = int(np.ceil((1.0+nfft)/2))
coln = int(np.fix((xlen-wlen)/h) + 1)
short_tft = np.zeros((rown,coln)).astype('complex64')
# initialize the indexes
indx = 0
col = 0
# perform STFT
while (indx + wlen <= xlen):
# windowing
xw =x[indx:indx+wlen]*win
# FFT
X = np.fft.fft(xw,nfft)
# update the stft matrix
short_tft[:,col] = X[0:rown]
# update the indexes
indx += h
col += 1
# calculate the time and frequency vectors
t = np.linspace(wlen/2,wlen/2+(coln-1)*h,coln)/fs
f = np.arange(0,rown,dtype= np.float32)*fs/nfft
return short_tft, f, t
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