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import numpy as np
import scipy
def spsi(msgram, fftsize, hop_length) :
"""
Takes a 2D spectrogram ([freqs,frames]), the fft length (= window length) and the hope size (both in units of samples).
Returns an audio signal.
"""
numBins, numFrames = msgram.shape
y_out=np.zeros(numFrames*hop_length+fftsize-hop_length)
#np.zeros(numFrames*hop_length+fftsize-hop_length)
m_phase=np.zeros(numBins);
m_win=scipy.signal.hanning(fftsize, sym=True) # assumption here that hann was used to create the frames of the spectrogram
#processes one frame of audio at a time
for i in range(numFrames) :
m_mag=msgram[:, i]
for j in range(1,numBins-1) :
if(m_mag[j]>m_mag[j-1] and m_mag[j]>m_mag[j+1]) : #if j is a peak
alpha=m_mag[j-1];
beta=m_mag[j];
gamma=m_mag[j+1];
denom=alpha-2*beta+gamma;
if(denom!=0) :
p=0.5*(alpha-gamma)/denom;
else :
p=0;
phaseRate=2*np.pi*(j+p)/fftsize; #adjusted phase rate
m_phase[j]= m_phase[j] + hop_length*phaseRate; #phase accumulator for this peak bin
peakPhase=m_phase[j];
# If actual peak is to the right of the bin freq
if (p>0) :
# First bin to right has pi shift
bin=j+1;
m_phase[bin]=peakPhase+np.pi;
# Bins to left have shift of pi
bin=j-1;
while((bin>1) and (m_mag[bin]<m_mag[bin+1])) : # until you reach the trough
m_phase[bin]=peakPhase+np.pi;
bin=bin-1;
#Bins to the right (beyond the first) have 0 shift
bin=j+2;
while((bin<(numBins)) and (m_mag[bin]<m_mag[bin-1])) :
m_phase[bin]=peakPhase;
bin=bin+1;
#if actual peak is to the left of the bin frequency
if(p<0) :
# First bin to left has pi shift
bin=j-1;
m_phase[bin]=peakPhase+np.pi;
# and bins to the right of me - here I am stuck in the middle with you
bin=j+1;
while((bin<(numBins)) and (m_mag[bin]<m_mag[bin-1])) :
m_phase[bin]=peakPhase+np.pi;
bin=bin+1;
# and further to the left have zero shift
bin=j-2;
while((bin>1) and (m_mag[bin]<m_mag[bin+1])) : # until trough
m_phase[bin]=peakPhase;
bin=bin-1;
#end ops for peaks
#end loop over fft bins with
magphase=m_mag*np.exp(1j*m_phase) #reconstruct with new phase (elementwise mult)
magphase[0]=0; magphase[numBins-1] = 0 #remove dc and nyquist
m_recon=np.concatenate([magphase,np.flip(np.conjugate(magphase[1:numBins-1]), 0)])
#overlap and add
m_recon=np.real(np.fft.ifft(m_recon))*m_win
y_out[i*hop_length:i*hop_length+fftsize]+=m_recon
return y_out
def magspect2audio(msgram, fftsize, hop_length) :
return spsi(msgram, fftsize, hop_length)
def logspect2audio(lsgram, fftsize, hop_length) :
return spsi(np.power(10, lsgram/20), fftsize, hop_length)
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