Question

I am trying to write an audio fingerprinting library for educational purpose. Its based on Computer Vision for Music Identification
. I have a couple of questions relating to the contents of the paper.

1. I know that two bytes represents a sample, so i wrote this class to extract the samples from a pcm file. I’d like to know if this is right (sorry if its too obvious 🙂 ).

   class FingerPrint:
   
      def __init__(self, pcmFile):
         self.pcmFile = pcmFile
         self.samples = []
         self.init()
   
   
      def init(self):
         # Current samples
         currentSamples = []
   
         # Read pcm file
         with open(self.pcmFile, 'rb') as f:
            byte = f.read(2)
            while byte != '':
              self.samples.append(byte)
              byte = f.read(2)
   
   fp = FingerPrint('output.pcm')
   

2. If the above code is ok, then according to the book the next thing to do is to convolve the signal with a low pass filter and take every 8th sample. I don’t understand these and why this has to be done, it would be awesome if someone could help me understand (with codes if possible)

Answer 1

After read the two bytes, you need to convert it into int. You can use struct module.

But I think you should use NumPy, SciPy:

To read wave file, you can call scipy.io.wavfile.read()

http://docs.scipy.org/doc/scipy-0.10.0/reference/tutorial/io.html#module-scipy.io.wavfile

If your file is raw PCM data, you can call numpy.fromfile()

http://docs.scipy.org/doc/numpy/reference/generated/numpy.fromfile.html

for example:

data = numpy.fromfile("test.pcm", dtype=np.int16)

To design lowpass filter, you can use filter design functions in scipy.signal:

http://docs.scipy.org/doc/scipy-0.10.1/reference/signal.html#filter-design

To do the convolve, you can use convoliving functions in scipy.signal:

http://docs.scipy.org/doc/scipy-0.10.1/reference/signal.html#convolution

There is also a convolve function in numpy:

http://docs.scipy.org/doc/numpy/reference/generated/numpy.convolve.html