Re-synchronization of independently-clocked audio streams by fading-in with a fractional sample over multiple periods for sample-rate conversion

摘要

A net sample is added or removed from an audio sample stream by fading in or out fractional samples over many sample periods. A sample-rate converter has a FIFO that is written with an input sample by an input clock synchronized to the input audio stream. The samples are read from the FIFO by a derived clock. The derived clock is generated from an output clock using a nominal ratio of Q/P. Read and write counters for the FIFO are compared. When the write counter is ahead of the read counter by exactly a target amount the derived clock is a ratio of Q/P of the output clock. When the write counter is ahead of the read counter by more than the target, the read rate is increased by removing one net sample over many sample periods. When the write counter is ahead of the read counter by less than the target amount, the read rate is decreased by adding one net sample over many sample periods. Samples from a delayed stream from the FIFO are faded in (out) by gradually increasing (decreasing) a weighting of successive fractional samples from the delayed stream and decreasing (increasing) the weighting of successive input-stream samples. Fade-in occurs over many sample periods, such as 256, to reduce audible distortion.