Fractional Delay Filters—Design and Applications

Abstract

In numerous applications, such as communications, audio and music technology, speech coding and synthesis, antenna and transducer arrays, and time delay estimation, not only the sampling frequency but the actual sampling instants are of crucial importance. Digital fractional delay (FD) filters provide a useful building block that can be used for fine-tuning the sampling instants, j .e., implement the required bandlimited interpolation. The FD filters can be designed and implemented flexibly using various established techniques that suit best for the particular application. In this review article, the generic problem of designing digital filters to approximate a fractional delay is addressed. We compare FIR and all-pass filter approaches to FD approximation. Time-and frequency-domain characteristics of various designs are shown to illustrate the nature of different approaches. Special attention is paid to time-varying FD filters and the elimination of induced transients. Also, nonuniform signal reconstruction using polynomial filtering techniques is discussed. Several applications, ranging from synchronization in digital communications to music synthesis, are described in detail. An extensive list of references is provided. v.