CiCueTea

Real-time, invertible Constant-Q Transform (CQT) engine based on nonstationary Gabor frames.

🍵 CiCueTea

CiCueTea *(pronounced "C-Q-T")* is a real-time, invertible Constant-Q Transform (CQT) engine based on nonstationary Gabor frames. This is the MATLAB reference implementation — dense and sparse forward/inverse transforms, sparse-to-dense rasterization, and the block slicing/splicing utilities for building a streaming pipeline. The real-time, allocation-free C++ engine and a Python reference implementation live at the linked GitHub repository.

🎧 "Brew your spectrum."

DOI: doi.org/10.5281/zenodo.21326372

Getting started

Open `GettingStarted.mlx` (bundled with this toolbox) for a runnable walkthrough — it

computes ERB-based and CQT-based transforms of an example signal and visualizes both the

analysis frame and the resulting time-frequency representation.

Functions

• nsgfCQTInit / nsgfVQTInit — initialize a nonstationary Gabor frame for the CQT / VQT
• nsgfCQT / nsgfICQT — forward / inverse transform (dense or sparse)
• nsgfRasterize — rasterize sparse coefficients into the dense matrix form
• slicer / splicer / spectralSlicer / spectralSplicer — block-streaming utilities

Citation

If you use CiCueTea in academic work, please cite it — see the repository's `CITATION.cff`.

This v1.0.0 release is archived at DOI 10.5281/zenodo.21326373

References

The theory behind CiCueTea — the pitch-symmetric log-Gaussian frame design and the real-time

implementation strategy — is developed in:

• J. Sierra, *Constant-Q Spectral Signal Processing*, Ph.D. dissertation, New York University, 2025.

Foundational literature on nonstationary Gabor frames and the invertible CQT:

• P. Balazs, M. Dörfler, F. Jaillet, N. Holighaus, and G. A. Velasco, "Theory, implementation and applications of nonstationary Gabor frames," *J. Comput. Appl. Math.*, 236(6), 2011.
• G. A. Velasco, N. Holighaus, M. Dörfler, and T. Grill, "Constructing an invertible constant-Q transform with nonstationary Gabor frames," *Proc. DAFx-11*, 2011.
• N. Holighaus, M. Dörfler, G. A. Velasco, and T. Grill, "A framework for invertible, real-time constant-Q transforms," *IEEE Trans. Audio, Speech, Lang. Process.*, 21(4), 2013.

MIT licensed.