This web-page accompanies the paper

Schörkhuber, C., Klapuri, A. "CONSTANT-Q TRANSFORM TOOLBOX FOR MUSIC PROCESSING," presented at the 7th Sound and Music Computing Conference , Barcelona, Spain, 2010
This paper proposes a computationally efficient method for computing the constant-Q transform (CQT) of a time- domain signal. CQT refers to a time-frequency represen- tation where the frequency bins are geometrically spaced and the Q-factors (ratios of the center frequencies to band- widths) of all bins are equal. An inverse transform is pro- posed which enables a reasonable-quality (around 55dB signal-to-noise ratio) reconstruction of the original signal from its CQT coefficients. Here CQTs with high Q-factors, equivalent to 12–96 bins per octave, are of particular inter- est. The proposed method is flexible with regard to the number of bins per octave, the applied window function, and the Q-factor, and is particularly suitable for the anal- ysis of music signals. A reference implementation of the proposed methods is published as a Matlab toolbox. The toolbox includes user-interface tools that facilitate spectral data visualization and the indexing and working with the data structure produced by the CQT.

Download the toolbox

A reference implementation of the proposed methods is available as a Matlab toolbox here.

Pitch shifting

The reference implementation also includes an exemplary implementation of a pitch transposition algorithm in the CQT domain as proposed in
Schörkhuber, C., Klapuri, A., and Sontacchi, A. " Audio Pitch Shifting Using the Constant-Q Transform," published in "Journal of the Audio Engineering Society", Vol. 61 (2013), Nr. 7/8, pp. 562-572
Schörkhuber, C., Klapuri, A., and Sontacchi, A. " Pitch shifting of audio signals using the constant-Q transform," submitted to the 15th International Conference on Digital Audio Effects DAFx-12 September 17-21, 2012 , York, UK.