Suppression of transients in time-varying recursive filters for audio signals

A new method for suppressing transients in time-varying recursive filters is proposed. The technique is based on modifying the state variables when the filter coefficients are changed so that the filter enters a new state smoothly without transient attacks, as originally proposed by Zetterberg and Zhang (1988). We modify the Zetterberg-Zhang algorithm to render it feasible for efficient implementation. We explain how to determine an optimal transient suppresser to cancel the transients down to a desired level with the minimum complexity of implementation. The application of the method to time-varying all-pole and direct form IIR filter structures is studied. The algorithm may be generalized for any recursive filter structure. The transient suppression technique finds applications in audio signal processing where the characteristics of a recursive filter needs to be changed in real time, such as in music synthesis, auralization, and equalization