Antialiasing filters for continuously varying sampling rate conversion

This paper discusses digital antialiasing filters for continuously varying, digitally implemented conversion of a digital signal from one input sampling rate to another output sampling rate. The scope of this paper includes cases where all sampling intervals of the output signal may differ from each other. A conversion factor which gives the number of input samples per one output sample might be a function of time or sample number, and may have a range which includes both integer and non-integer values. As a time function, a conversion factor may be discontinuous or continuous (if quantization is ignored). There is a limited degree of freedom in selecting structures for antialiasing filters for continuously varying rate conversion. A class of low-pass FIR filters for that purpose is described here. The filters provide a specified antialiasing rejection in a stop-band, and have an impulse response which tracks the output. sampling rate. This tracking means that the continuously varying rate conversion, while being a translation-variant system in the time domain (time-variance) or in the input sample number domain, is translation-invariant in the output sample number domain.