This analogy also works for a delay-line based computational model. The magnetic tape is now the delay line, the tape read-head is the read-pointer of the delay line, and the write-head is the delay-line write-pointer. In this analogy, it is readily verified that modulating delay by changing the read-pointer increment from 1 to (thereby requiring interpolated reads) corresponds to listener motion away from the source at speed . It also follows that changing the write-pointer increment from to corresponds source motion toward the listener at speed .When this is done, we must use interpolating writes into the delay memory. Interpolating writes are often called de-interpolation , and they are formally the graph-theoretic transpose of interpolating reads (ordinary ``interpolation'') . A review of time-varying, interpolating, delay-line reads and writes, together with a method using a single shared pointer, are given in .