Filter transitions in adaptive IIR approximate filtering

The effects associated with the switching of filter orders in an incrementally adaptive IIR approximate filtering technique are evaluated in the context of speech signals. Through listening experiments, we have found that the perceptual quality of the speech at the filter output is sensitive to the initial conditions used in initiating a transition to a higher filter order. If zero initial conditions are used there is a significant crackling sound due to error bursts at points where switches to higher order filters take place. If output samples from the pre-transition filter are used as initial conditions for the post-transition filter, the amplitude of the error bursts decreases significantly. An analysis is presented to account for these observations.