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PyMIR is a Python library for common tasks in Music Information Retrieval (MIR)



  • Read WAV files (using scipy) and MP3 files (using FFmpeg)
  • Temporal feature extraction (Frame class)
    • Constant-Q Transform
    • Discrete Cosine Transform
    • Energy
    • Frame segmentation from onsets
    • RMS
    • Spectrum (FFT)
    • Zero-crossing rate
  • Spectral feature extraction (Spectrum class)
    • Spectral Centroid
    • Spectral Flatness
    • Spectral Moments (mean, variance, skewness, kurtosis)
    • Spectral Spread
    • Spectral Rolloff
    • Spectral Crest Factor
    • Chroma
    • Inverse Discrete Cosine Transform
    • Inverse FFT
  • Other features
    • Audio playback via PyAudio
    • Naive chord estimation
    • Naive pitch estimation
    • Onset detectors (energy, flux)
    • Spectral Flux


The standard workflow for working with PyMIR is:

  • Open an audio file (wav or mp3)
  • Decompose into frames
    • Decomposed into fixed-size frames or
    • Use an onset detector
  • Extract temporal features
  • Extract spectral features

Opening an audio file (AudioFile class)

from pymir import AudioFile
wavData ="audio.wav")
mp3Data ="audio.mp3")

Decomposing into frames

Fixed frame size

fixedFrames = wavData.frames(1024)

windowFunction = numpy.hamming
fixedFrames = audiofile.frames(1024, windowFunction)

Using an onset detector

from import onsets
energyOnsets = onsets.onsetsByEnergy(wavData)
framesFromOnsets = wavData.framesFromOnsets(energyOnsets)

Extracting temporal features (Frame class)

fixedFrames[0].cqt()                        # Constant Q Transform
fixedFrames[0].dct()                        # Discrete Cosine Transform
fixedFrames[0].energy(windowSize = 256)     # Energy
fixedFrames[0].play()                       # Playback using pyAudio
fixedFrames[0].plot()                       # Plot using matplotlib
fixedFrames[0].rms()                        # Root-mean-squared amplitude
fixedFrames[0].zcr()                        # Zero-crossing raate

Extracting spectral features

# Compute the spectra of each frame
spectra = [f.spectrum() for f in fixedFrames]
spectra[0].centroid()                       # Spectral Centroid
spectra[0].chroma()                         # Chroma vector
spectra[0].crest()                          # Spectral Crest Factor
spectra[0].flatness()                       # Spectral Flatness
spectra[0].idct()                           # Inverse DCT
spectra[0].ifft()                           # Inverse FFT
spectra[0].kurtosis()                       # Spectral Kurtosis
spectra[0].mean()                           # Spectral Mean
spectra[0].mfcc2()                          # MFCC (vectorized implementation)
spectra[0].plot()                           # Plot using matplotlib
spectra[0].rolloff()                        # Spectral Rolloff
spectra[0].skewness()                       # Spectral Skewness
spectra[0].spread()                         # Spectral Spread
spectra[0].variance()                       # Spectral Variance

from pymir import SpectralFlux

# Compute the spectral flux
flux = SpectralFlux.spectralFlux(spectra, rectify = True)

Audio playback

Playback is provided on all AudioFile and Frame objects. Internal representation is 32-bit floating point.

Naive chord estimation

Naive chord estimation using a dictionary of the 24 major and minor triads only, represented as normalized chroma vectors. Similarity is measured using the cosine similarity function. The closest match is returned (as a string).

This is called a naive approach because it does not consider preceding chords, which could improve chord estimation accuracy.

To use, compute the chroma vector from a spectrum, and then use the getChord method

spectrum = frame.spectrum()
chroma = spectrum.chroma()
chord = chordestimator.getChord(chroma)
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