Reading *.wav files in Python

I need to analyze sound written in a .wav file. For that I need to transform this file into set of numbers (arrays, for example). I think I need to use the wave package. However, I do not know how exactly it works. For example I did the following:

import wave
w = wave.open('/usr/share/sounds/ekiga/voicemail.wav', 'r')
for i in range(w.getnframes()):
    frame = w.readframes(i)
    print frame

As a result of this code I expected to see sound pressure as function of time. In contrast I see a lot of strange, mysterious symbols (which are not hexadecimal numbers). Can anybody, pleas, help me with that?

Solution 1:

Per the documentation, scipy.io.wavfile.read(somefile) returns a tuple of two items: the first is the sampling rate in samples per second, the second is a numpy array with all the data read from the file:

from scipy.io import wavfile
samplerate, data = wavfile.read('./output/audio.wav')

Solution 2:

Using the struct module, you can take the wave frames (which are in 2's complementary binary between -32768 and 32767 (i.e. 0x8000 and 0x7FFF). This reads a MONO, 16-BIT, WAVE file. I found this webpage quite useful in formulating this:

import wave, struct

wavefile = wave.open('sine.wav', 'r')

length = wavefile.getnframes()
for i in range(0, length):
    wavedata = wavefile.readframes(1)
    data = struct.unpack("<h", wavedata)
    print(int(data[0]))

This snippet reads 1 frame. To read more than one frame (e.g., 13), use

wavedata = wavefile.readframes(13)
data = struct.unpack("<13h", wavedata)

Solution 3:

Different Python modules to read wav:

There is at least these following libraries to read wave audio files:

• SoundFile
• scipy.io.wavfile (from scipy)
• wave (to read streams. Included in Python 2 and 3)
• scikits.audiolab (unmaintained since 2010)
• sounddevice (play and record sounds, good for streams and real-time)
• pyglet
• librosa (music and audio analysis)
• madmom (strong focus on music information retrieval (MIR) tasks)

The most simple example:

This is a simple example with SoundFile:

import soundfile as sf
data, samplerate = sf.read('existing_file.wav') 

Format of the output:

Warning, the data are not always in the same format, that depends on the library. For instance:

from scikits import audiolab
from scipy.io import wavfile
from sys import argv
for filepath in argv[1:]:
    x, fs, nb_bits = audiolab.wavread(filepath)
    print('Reading with scikits.audiolab.wavread:', x)
    fs, x = wavfile.read(filepath)
    print('Reading with scipy.io.wavfile.read:', x)

Output:

Reading with scikits.audiolab.wavread: [ 0.          0.          0.         ..., -0.00097656 -0.00079346 -0.00097656]
Reading with scipy.io.wavfile.read: [  0   0   0 ..., -32 -26 -32]

SoundFile and Audiolab return floats between -1 and 1 (as matab does, that is the convention for audio signals). Scipy and wave return integers, which you can convert to floats according to the number of bits of encoding, for example:

from scipy.io.wavfile import read as wavread
samplerate, x = wavread(audiofilename)  # x is a numpy array of integers, representing the samples 
# scale to -1.0 -- 1.0
if x.dtype == 'int16':
    nb_bits = 16  # -> 16-bit wav files
elif x.dtype == 'int32':
    nb_bits = 32  # -> 32-bit wav files
max_nb_bit = float(2 ** (nb_bits - 1))
samples = x / (max_nb_bit + 1)  # samples is a numpy array of floats representing the samples