On Sample Rate Conversion Based on Variable Fractional Delay Filters

The sample rate conversion algorithm based on variable fractional delay filters is often used if the resampling ratio cannot be expressed as the ratio of small integer numbers or if it is not constant. The main advantage of such solution is that it allows for arbitrary resampling ratios which can even be changed during the resampling process. In this paper a discussion on influence of different approaches to fractional filter design on performance of sample rate conversion algorithm implemented using variable fractional delay filters is presented. Since the performance of such resampling algorithm depends solely on the method used to design fractional delay filters, we present its properties in relation to the presented classification of fractional delay filter design methods. The proposed general categories of fractional filter design are: optimal design, offset window method and polyphase decomposition.