Read wav file into python

Question

I'm trying to read in a wav file to run an fft on it but I keep running into an error with scipy.

import matplotlib.pyplot as plt
from scipy.io import wavfile as wav
import scipy    
from scipy.fftpack import fft
import numpy as np

rate, data = scipy.io.wavfile.read('a1.wav')
fft_out = fft(data)
#matplotlib inline
plt.plot(data, np.abs(fft_out))
plt.show()
print 'exit'

The error I'm running into is:

Traceback (most recent call last):
    File "test.py", line 9, in <module>
        rate, data = scipy.io.wavfile.read('a1.wav')
    File "/usr/local/lib/python2.7/site-packages/scipy/io/wavfile.py", line 275, in read
        return fs, data
UnboundLocalError: local variable 'data' referenced before assignment

I thought it might have been an anaconda error so I removed anaconda but I'm still running into this issue.

If there is a better way to read wav files so that I can run ffts on them, let me know! Thanks!

which version of scipy are we talking about? Can you try the lastest one and see if the error persists — cel
– cel, Commented Jan 21, 2017 at 17:15
Can you try loading a different WAV file? The problem might be specific to a1.wav. — wildwilhelm
– wildwilhelm, Commented Jan 21, 2017 at 17:21
You could try running the software available at mediaarea.net/en/MediaInfo to see if it exposes anything about that file. — Bill Bell
– Bill Bell, Commented Jan 21, 2017 at 17:27

J. P. Petersen · Accepted Answer · 2017-01-22 08:02:42Z

If you look at the code of the particular wavefile.read() here on Github, you'll see that data is only set in one place in the function:

        elif chunk_id == b'data':
            if not fmt_chunk_received:
                raise ValueError("No fmt chunk before data")
            data = _read_data_chunk(fid, format_tag, channels, bit_depth,
                                    is_big_endian, mmap)

So this condition is never met when the Python interpreter runs the code, and we get the referenced before assignment exception.

A wav file consist of a header followed by a sequence of chunks. There are different types of chuncks. For example one can carry information about the data format, another the sampling rate, and then there is the one that contains the data. It seems in this case that Scipy's read newer encounters this datachunck, so it is very likely that there is something wrong with the wav file, or it might be of some newer format, which Scipy's implementation does not yet support.

Jagesh Maharjan · Accepted Answer · 2018-05-24 07:11:55Z

0

Could it be becuse you need sox package. if so, try installing sox. apt install sox Also, check the header of the audio files,

soxi file_1.wav

and

apt install libav-tools
apt install ffmpeg

edited May 24, 2018 at 7:11

answered May 24, 2018 at 7:06

Jagesh Maharjan

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