PyMIR

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

Prerequisites

• Numpy
• Scipy
• FFmpeg executable
• PyAudio (for playback)
• Matplotlib (for graphing)

Features

• 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

Examples

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 = AudioFile.open("audio.wav")
mp3Data = AudioFile.open("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 pymir.audio 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.

wavData.play()
fixedFrames[0].play()

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)