The design of an asynchronous digital sample-rate converter for digital-audio applications is presented. The theory of asynchronous sample-rate conversion is discussed using a signal-processing model that is based on highly interpolated input samples. A novel closed-loop address-tracking system is disclosed that solves the problem of clock-edge arrival estimation while at the same time providing a low-jitter selection of the correct polyphase filter for each output sample. Sample-rate ratio changes of up to 2:1 in either direction can be accommodated. The proposed signal-processing algorithm has been implemented in a 0.8-µm CMOS technology. Measurement results show excellent agreement with theory.