Approximating sample rate conversion system

摘要

A sample rate conversion system converts from an input sample rate stream having a predetermined input sample rate to an output sample stream having a predetermined output sample rate by interpolating output samples from the input samples using first and second approximate sample rate ratios. The system includes circuitry which selects a sequence of interpolation filters from among a set of filters, the sequences being defined by one of these approximate ratios, and circuitry which monitors the magnitude of the accumulated error introduced by the approximation. When this accumulated error becomes greater than a threshold, the system changes to use a further sequence of interpolation filters based on the other approximate ratio. The accumulated error changes in a positive sense with each successive sample while one of the two approximate ratios is used. The accumulated error changes in a negative sense with each successive sample while the other of the two approximate ratios is used. The system switches between these sample rate ratios to maintain the magnitude of the position error of the interpolated samples below a predetermined threshold value. A sample rate conversion system which converts a television signal in CCIR (601) format into a Phase Alternate Line (PAL) video signal is disclosed.