Introduction to Audio in Python

import scikits.audiolab as audiolab

import pylab as plt

import numpy as np

# create Sndfile instance with our example audio file

f = audiolab.Sndfile('viola.wav', 'r')

#################

## Extracting metadata from audio file

#################

# sample rate

fs = f.samplerate

print "Sample rate: ", fs

# number of channels

nc = f.channels

print "Number of channels: ", nc

# encoding format

enc = f.encoding

print "Encoding format: ", enc

# number of frames - single samples for

# mono and pairs of samples for stereo

num_samples = f.nframes

#################

## Reading Audio Samples from the file

#################

# We can read audio samples using the read_frame method

samples = f.read_frames(num_samples)

# We can now close the file...

f.close()

#################

## Playing the audio

#################

# play the audio file data in 'samples' at the sampling frequency 'fs'

audiolab.play(samples,fs)

#################

## Choosing only the first half second of audio

#################

# the new number of samples is the

# (duration times sampling frequency)

new_nsamples = 0.5 * fs

# creating the new samples array

new_samples = samples[0:new_nsamples]

#################

## Plotting the new signal using pylab/matplotlib

#################

# the x axis now shows the time in seconds instead of the sample number

## using the Numpy function linspace in order to create the time array

x_axis = np.linspace(0, 0.5, new_samples.size)

plt.plot(x_axis, new_samples)

plt.show()

#################

## Writing the shorter audio to a new file

#################

# create a name for the new file

new_filename = 'output_file.wav'

# Create a Sndfile instance for writing a mono wav file @ 44100 Hz

format = audiolab.Format('wav')

f = audiolab.Sndfile(new_filename, 'w', format, 1, 44100)

# Write out the shorter audio file

f.write_frames(new_samples)

# close the audio file

f.close()