Smooth and Safe Parameter Interpolation of Biquadratic Filters in Audio Applications

Parameter interpolation (PI) of biquadratic IIR filters (biquads) is widely used in audio applications to avoid very undesirable audible effects like plops, clicks etc. It is shown that although the simplest linear PI of numerator and denominator coefficients of the transfer function of a biquad guarantees the stability it, however, may sometimes lead to other audible side effects caused, for example, by the possible growth of the magnitude response at some frequencies in some intermediate states of PI procedure. To avoid audible transients and to make the PI easily portable into digital signal processor (DSP) a special technique is applied called here “sliding edges”. The detailed description of this technique and their comparison is the goal of the present paper.