We will mainly use three libraries for audio acquisition and playback: IPython.display.Audio, essentia.standard, and librosa.
Introduced in IPython 2.0, IPython.display.Audio lets you play audio directly in an IPython notebook.
Essentia is an open-source library for audio analysis and music information retrieval from the Music Technology Group at Universitat Pompeu Fabra. Although Essentia is written in C++, we will use the Python bindings for Essentia.
librosa is a Python package for music and audio processing by Brian McFee. A large portion was ported from Dan Ellis's Matlab audio processing examples.
To download a file onto your local machine (or Vagrant box) in Python, you can use urllib.urlretrieve:
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import urllib
urllib.urlretrieve('https://ccrma.stanford.edu/workshops/mir2014/audio/simpleLoop.wav', filename='simpleLoop.wav')
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To check that the file downloaded successfully, list the files in the working directory:
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%ls *.wav
Visit https://ccrma.stanford.edu/workshops/mir2014/audio/ for more audio files.
If you only want to listen to, and not manipulate, a remote audio file, use IPython.display.Audio instead. (See Playing Audio.)
MonoLoader reads (and downmixes, if necessary) an audio file into a single channel (as will often be the case during this workshop). MonoLoader also resamples the audio to a sampling frequency of your choice (default = 44100 Hz):
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from essentia.standard import MonoLoader
audio = MonoLoader(filename='simpleLoop.wav')()
audio.shape
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N = len(audio)
t = arange(0, N)/44100.0
plot(t, audio)
xlabel('Time (seconds)')
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For more control over the audio acquisition process, you may want to use AudioLoader instead.
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import librosa
x, fs = librosa.load('simpleLoop.wav')
print x.shape
print fs
Using IPython.display.Audio, you can play a local audio file or a remote audio file:
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from IPython.display import Audio
Audio('https://ccrma.stanford.edu/workshops/mir2014/audio/CongaGroove-mono.wav') # remote WAV file
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Audio('simpleLoop.wav') # local WAV file
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Audio can also accept a NumPy array:
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fs = 44100 # sampling frequency
T = 1.5 # seconds
t = numpy.linspace(0, T, int(T*fs), endpoint=False) # time variable
x = numpy.sin(2*numpy.pi*440*t) # pure sine wave at 440 Hz
Audio(x, rate=fs)
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To play audio from the command line, we recommend SoX (included in the stanford-mir Vagrant box).
$ play simpleLoop.wavplot is the simplest way to plot time-domain signals:
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T = 0.001 # seconds
fs = 44100 # sampling frequency
t = numpy.linspace(0, T, int(T*fs), endpoint=False) # time variable
x = numpy.sin(2*numpy.pi*3000*t)
plot(t, x)
xlabel('Time (seconds)')
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specgram is a Matplotlib tool for computing and displaying spectrograms.
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S, freqs, bins, im = specgram(x, NFFT=1024, Fs=fs, noverlap=512)
xlabel('Time')
ylabel('Frequency')
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MonoWriter can write a NumPy array to a WAV file. Note: the array must have type int, single, or complex64.
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from essentia.standard import MonoWriter
noise = 0.1*randn(44100)
MonoWriter(filename='noise1.wav')(single(noise))
%ls *.wav
librosa.output.write_wav also saves a NumPy array to a WAV file. This is a bit easier to use.
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import librosa
noise = 0.1*randn(44100)
librosa.output.write_wav('noise2.wav', noise, 44100)
%ls *.wav