A Matlab Toolbox for Efficient Perfect Reconstruction Time-Frequency Transforms with Log-Frequency Resolution

Introduction

This web-page accompanies the paper

Schörkhuber, C., Klapuri, N. Holighaus, and M. Döfler, "A Matlab Toolbox for Efficient Perfect Reconstruction Time-Frequency Transforms with Log-Frequency Resolution," submitted to the AES 53rd International Conference on Semantic Audio, London, UK
Abstract:
In this paper, we propose a time-frequency representation where the frequency bins are distributed uniformly in log-frequency and their Q-factors obey a linear function of the bin center frequencies. The latter allows for time-frequency representations where the bandwidths can be e.g. constant on the log-frequency scale (constant Q) or constant on the auditory critical-band scale (smoothly varying Q). The proposed techniques are published as a Matlab toolbox that extends [1]. Besides the features that stem from [1], perfect reconstruction and computational effciency, we propose here a technique for computing coefficient phases in a way that makes their interpretation more natural. Other extensions include flexible control of the Q- values and more regular sampling of the time-frequency plane in order to simplify signal processing in the transform domain.

Download the toolbox

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

Pitch shifting

The reference implementation includes the file PITCHSHIFTING.m where the process of transpositions in the CQT domain is demonstrated. More information on pitch shifting using the CQT can be found 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
and
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.