Method and apparatus for processing discontinuities in digital sound signals caused by pitch control

摘要

Small discontinuities in digital sound data caused by a pitch control operation are processed by using a secondary FIR filter and smoothing the discontinuities. When lowering the key, the data value subject to the pitch down operation is moderately approximated to that of one sampling period before over a cycle of small discontinuity occurrence. when raising the key, the data value subject to the pitch up operation is moderately approximated to the current data value over a cycle of small discontinuity occurrence. By this method, the extent of the data discontinuity is greatly reduced. Large discontinuities for every segment are also processed by cross fading two converted data sequences which are produced from the input sound data and have different timings of large discontinuity occurrence, one data value being increased from its discontinuity point while the other data value is decreased from the same point in time. The weighting coefficients for the cross fade process vary in time along an upwardly convex polygonal line or a 1/4 cycle of a sine curve, thereby reducing the extent of the large discontinuity and avoiding the offset of the overlapped two data values.