The Doppler effect causes a source signal to appear as though it has been pitch shifted. Pitch shifting of an input signal can thus be implemented with time-varying delay lines as described above.
Because the read pointer of a pitch shifter is incremented at a constant non-integer rate, the read pointer will eventually “catch up to” or “fall back into” the write pointer location. To avoid discontinuity issues caused when the read and write pointers cross, a multiple read pointer cross-fade system can be used.