Wavelet transform library

Upstream URL


Vasily Postnicov <>


2-clause BSD


Build Status CI

cl-wavelets is a library with a set of algorithms related to various kinds of wavelet transform. Currently they all work with arrays of type (simple-array (signed-byte 32) (*)) (i.e. they are 1D). This makes this library suitable for audio processing and compression. For more info visit the project page here.

Currently supported algorithms:

  • DWT
  • Frequency analysis using PWT.
  • Best-basis PWT.

Currently supported wavelets:

  • Haar wavelet
  • CDF (2,2) wavelet
  • CDF (3,1) wavelet
  • CDF (4,2) wavelet


In examples:

(wavelets:dwt (make-array 8
                          :element-type     '(signed-byte 32)
                          :initial-contents '(0 1 2 3 4 5 7 8))
              :wavelet        :cdf-2-2
              :boundary-style :mirror)
#(2 4 0 3 0 0 0 1)

(wavelets:dwt-inverse *
                      :wavelet        :cdf-2-2
                      :boundary-style :mirror)
#(0 1 2 3 4 5 7 8)

Generally, there are two kinds of functions: with ! at the end and without !. Whose with ! are in-place functions, in other words they modify their first argument. Whose without ! do not modify their first argument.

For more info, generate a documentation with codex like so: codex:document :cl-wavelets :skip-unsocumented t.

Examples package

You can load cl-wavelets/examples system which contains packages to demonstrate some components of this library. For example, you can build a spectrogram of an uncompressed WAV file making use of wavelets:frequency-domain function. To build a spectrogram, try this:

(wavelets-spectrogram:spectrogram "/path/to/audio.wav"

This will produce spectrogram.jpg image with the spectrogram. Note, that the time axis is the vertical one, with the time going up-down. This is a spectrogram rotated by 90 degrees clockwise, actually. Also, the quality of the spectrogram will be much worse compared to the qualily of a spectrogram obtained via FFT. This is because the filters used in the process are far from ideal.

Dependencies (5)

  • alexandria
  • cl-jpeg
  • easy-audio
  • fiveam
  • serapeum

Dependents (0)

    • GitHub
    • Quicklisp