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Applications of a Constant-Q Transform for Time- and Pitch-Scale Modifications

Authors Schörkhuber, C.
Year 2012
Thesis Type Diploma thesis
Topic Audio Signal Processing
Keywords Klangsynthese, musical acoustics, Aufnahme- und Wiedergabetechnik
Abstract Modifications of the time- and pitch-scale of polyphonic music are usually performed by manipulating the time-frequency representation of an audio signal. Most of the approaches proposed in the past are thereby based on the short-time Fourier transform (STFT) although its linear frequency bin spacing is known to be inadequate to some degree for analyzing and processing music signals. For this signal class the constant-Q transform (CQT) is superior to the STFT as it features a geometrical bin spacing and high Q- factors (typically equivalent to 12-96 bins per octave). In music processing applications, however, the CQT has been playing only a minor role due to its computational complexity and the lack of an inverse transform. Recently, solutions to these problems have been proposed, thus rendering the CQT a feasible alternative to the STFT for music processing applications. In this thesis time- and pitch-scaling algorithms based on the CQT representation of music signals are proposed that improve upon the quality achieved by simple STFT based approaches.
Supervisors Sontacchi, A., Klapuri, A.