Modified phase vocoder scheme for dynamic frequency warping

Frequency warping is a desirable building block for sound effects and synthesis. Physical model driven pitch shifting of inharmonic sounds and the transformation of harmonic into inharmonic sounds are the main features of frequency warping effects. However, frequency warping sound signals is a non-causal and computationally expensive operation. In recent work [G. Evangelista and S. Cavaliere, 2007] we showed that multirate filter banks derived from a modified phase vocoder structure are suitable for the real-time approximate computation of frequency warping. The approximation is proven to be very accurate from both numerical and perceptual points of view. In this paper we extend the principles of the original design to implement time-varying frequency warping methods. The proposed algorithm is suitable for inclusion in the synthesis of systems with dynamic stiffness and for the production of captivating audio effects.