Added the simplest implementation of Paulstretch algorithm.

paulstretch_mono.py

@@ -0,0 +1,115 @@
+#
+# Paul's Extreme Sound Stretch (Paulstretch) - Python version
+#
+# by Nasca Octavian PAUL, Targu Mures, Romania
+#
+# http://hypermammut.sourceforge.net/paulstretch/
+#
+#
+
+
+import sys
+from numpy import *
+import scipy.io.wavfile
+import wave
+
+def load_wav(filename):
+    try:
+        wavedata=scipy.io.wavfile.read(filename)
+        samplerate=int(wavedata[0])
+        smp=wavedata[1]*(1.0/32768.0)
+        if len(smp.shape)>1: #convert to mono
+            smp=(smp[:,0]+smp[:,1])*0.5
+        return (samplerate,smp)
+    except:
+        print "Error loading wav: "+filename
+        return None
+
+
+
+########################################
+
+def paulstretch(samplerate,smp,stretch,windowsize_seconds,outfilename):
+    outfile=wave.open(outfilename,"wb")
+    outfile.setsampwidth(2)
+    outfile.setframerate(samplerate)
+    outfile.setnchannels(1)
+
+    #make sure that windowsize is even and larger than 16
+    windowsize=int(windowsize_seconds*samplerate)
+    if windowsize<16:
+        windowsize=16
+    windowsize=int(windowsize/2)*2
+    half_windowsize=int(windowsize/2)
+
+    #correct the end of the smp
+    end_size=int(samplerate*0.05)
+    if end_size<16:
+        end_size=16
+    smp[len(smp)-end_size:len(smp)]*=linspace(1,0,end_size)
+
+
+    #compute the displacement inside the input file
+    start_pos=0.0
+    displace_pos=(windowsize*0.5)/stretch
+
+    #create Hann window
+    window=0.5-cos(arange(windowsize,dtype='float')*2.0*pi/(windowsize-1))*0.5
+
+    old_windowed_buf=zeros(windowsize)
+    hinv_sqrt2=(1+sqrt(0.5))*0.5
+    hinv_buf=hinv_sqrt2-(1.0-hinv_sqrt2)*cos(arange(half_windowsize,dtype='float')*2.0*pi/half_windowsize)
+
+    while True:
+
+        #get the windowed buffer
+        istart_pos=int(floor(start_pos))
+        buf=smp[istart_pos:istart_pos+windowsize]
+        if len(buf)<windowsize:
+            buf=append(buf,zeros(windowsize-len(buf)))
+        buf=buf*window
+
+        #get the amplitudes of the frequency components and discard the phases
+        freqs=abs(fft.rfft(buf))
+
+        #randomize the phases by multiplication with a random complex number with modulus=1
+        ph=random.uniform(0,2*pi,len(freqs))*1j
+        freqs=freqs*exp(ph)
+
+        #do the inverse FFT 
+        buf=fft.irfft(freqs)
+
+        #window again the output buffer
+        buf*=window
+
+
+        #overlap-add the output
+        output=buf[0:half_windowsize]+old_windowed_buf[half_windowsize:windowsize]
+        old_windowed_buf=buf
+
+        #remove the resulted amplitude modulation
+        output*=hinv_buf
+
+        #clamp the values to -1..1 
+        output[output>1.0]=1.0
+        output[output<-1.0]=-1.0
+
+        #write the output to wav file
+        outfile.writeframes(int16(output*32767.0).tostring())
+
+        start_pos+=displace_pos
+        if start_pos>=len(smp):
+            print "100 %"
+            break
+        print "%d %% \r" % int(100.0*start_pos/len(smp)),
+        sys.stdout.flush()
+
+    outfile.close()
+########################################
+
+(samplerate,smp)=load_wav("input.wav")
+
+paulstretch(samplerate,smp,8.0,0.25,"out.wav")
+
+
+