Announcing a new 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. The Constant-Q is useful as a preliminary transform in various other methods such as note transcription and key estimation techniques. 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 code is provided with full source under a liberal licence, and plugin binaries are provided for Windows, OS/X, and Linux. 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.