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Constant-Q Library
==================

A C++ library and Vamp plugin implementing the Constant-Q transform
of a time-domain signal.

https://code.soundsoftware.ac.uk/projects/constant-q-cpp

The Constant-Q transform is a time-to-frequency-domain transform
related to the short-time Fourier transform, but with output bins
spaced logarithmically in frequency, rather than linearly. The output
bins are therefore linearly spaced in terms of musical pitch.

This library provides:

 * Forward transform: time-domain to complex Constant-Q bins
 * Forward spectrogram: time-domain to interpolated Constant-Q
   magnitude spectrogram
 * Inverse transform: complex Constant-Q bins to time domain

The Vamp plugin provides:

 * Constant-Q magnitude spectrogram with high and low frequency
   extents defined in Hz
 * Constant-Q magnitude spectrogram with high and low frequency
   extents defined as MIDI pitch values
 * Pitch chromagram obtained by folding a Constant-Q spectrogram
   around into a single-octave range

The method is drawn from Christian Schörkhuber and Anssi Klapuri,
"Constant-Q transform toolbox for music processing", SMC 2010. See the
file CITATION for details. If you use this code in research work,
please cite this paper.

The implementation is reasonably fast and is causal, operating
block-by-block on the input, though with quite high latency
depending on the frequency range specified. By default it produces
output at a higher time resolution than some other implementations,
using multiple kernel atoms per time block. The inverse transform is
approximate rather than exact (see the paper for details).

The C++ implementation is by Chris Cannam, Copyright 2014-2015 Queen
Mary, University of London.

The library is provided under a liberal BSD/MIT-style open source
licence. See the file COPYING for more information.