plot spectogram from mp3

prerequisites

install libav

use homebrew $ brew install libav

      $ brew install libav
      ==> Installing dependencies for libav: faac, lame, x264, xvid
      ==> Installing libav dependency: faac
      ==> Downloading https://homebrew.bintray.com/bottles/faac-1.28.yosemite.bottle.1.tar.gz
      ######################################################################## 100.0%
      ==> Pouring faac-1.28.yosemite.bottle.1.tar.gz
      🍺  /usr/local/Cellar/faac/1.28: 13 files, 712K
      ==> Installing libav dependency: lame
      ==> Downloading https://homebrew.bintray.com/bottles/lame-3.99.5.yosemite.bottle.1.tar.gz
      ######################################################################## 100.0%
      ==> Pouring lame-3.99.5.yosemite.bottle.1.tar.gz
      🍺  /usr/local/Cellar/lame/3.99.5: 25 files, 2.1M
      ==> Installing libav dependency: x264
      ==> Downloading https://homebrew.bintray.com/bottles/x264-r2533.yosemite.bottle.tar.gz
      ######################################################################## 100.0%
      ==> Pouring x264-r2533.yosemite.bottle.tar.gz
      🍺  /usr/local/Cellar/x264/r2533: 9 files, 3.4M
      ==> Installing libav dependency: xvid
      ==> Downloading https://homebrew.bintray.com/bottles/xvid-1.3.3.yosemite.bottle.2.tar.gz
      ######################################################################## 100.0%
      ==> Pouring xvid-1.3.3.yosemite.bottle.2.tar.gz
      🍺  /usr/local/Cellar/xvid/1.3.3: 9 files, 1.3M
      ==> Installing libav
      ==> Downloading https://homebrew.bintray.com/bottles/libav-11.3.yosemite.bottle.tar.gz
      ######################################################################## 100.0%
      ==> Pouring libav-11.3.yosemite.bottle.tar.gz
      🍺  /usr/local/Cellar/libav/11.3: 8 files,  18M

code from stackoverflow

        import os
        from subprocess import check_call
        from tempfile import mktemp
        from scikits.audiolab import wavread, play
        from scipy.signal import remez, lfilter
        from pylab import *

        # convert mp3, read wav
        mp3filename = 'quit.playing.games.mp3'
        wname = mktemp('.wav')
        check_call(['/usr/local/bin/avconv', '-i', mp3filename, wname])
        sig, fs, enc = wavread(wname)
        os.unlink(wname)

        # bandpass filter
        bands = array([0,3500,4000,5500,6000,fs/2.0]) / fs
        desired = [0, 1, 0]
        b = remez(513, bands, desired)
        sig_filt = lfilter(b, 1, sig)
        sig_filt /=  1.05 * max(abs(sig_filt)) # normalize

        subplot(211)
        specgram(sig, Fs=fs, NFFT=1024, noverlap=0)
        axis('tight'); axis(ymax=8000)
        title('Original')
        subplot(212)
        specgram(sig_filt, Fs=fs, NFFT=1024, noverlap=0)
        axis('tight'); axis(ymax=8000)
        title('Filtered')
        show()

        play(sig_filt, fs)

api

scipy.signal.remez
- scipy.signal.remez(numtaps, bands, desired, weight=None, Hz=1, type=’bandpass’, maxiter=25, grid_density=16)[source]
- reference
scipy.signal.lfilter
- scipy.signal.lfilter(b, a, x, axis=-1, zi=None)

todo 1

there is still some error here

      check_call(['avconv', '-i', mp3filename, wname])

      raise child_exception

      OSError: [Errno 2] No such file or directory

solution

use full path of avconv

  $ which avconv
  /usr/local/bin/avconv

run check_call

  In [4]: from subprocess import check_call
     ...: from tempfile import mktemp
     ...: mp3filename = 'quit.playing.games.mp3'
     ...: wname = mktemp('.wav')
     ...: check_call(['/usr/local/bin/avconv', '-i', mp3filename, wname])
     ...:

  Out[4]: 0

reference

todo 2

problem

      Traceback (most recent call last):

        File "<ipython-input-6-42c328711091>", line 20, in <module>
          sig_filt /=  1.05 * max(abs(sig_filt)) # normalize

      ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

solution