Design of Variable Bandpass Filters Using First Order Allpass Transformation And Coefficient Decimation

Abstract: In this paper, the design of a computationally efficient variable bandpass digital filter is presented. The center frequency and bandwidth of this filter can be changed online without updating the filter coefficients. The warped filters, obtained by replacing each unit delay of a digital filter with an allpass filter, are widely used for various audio processing applications. However, warped filters fail to provide variable bandwidth bandpass responses for a given center frequency using first order allpass transformation. To overcome this drawback, our design is accomplished by combining warped filter with the coefficient decimation technique. The design example shows that the proposed variable digital filter is simple to design and offers a total gate count reduction of 36% and 65% over the warped filters compared to the designs presented in [3] and [1] respectively