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Delta Modulation (DM) 621
FIGURE 12.11
An example of a delta modulation system with adaptive step size
where K ≥ 1isaconstant that is selected to minimize the total distortion.
A block diagram of a DM encoder-decoder that incorporates this adaptive
algorithm is illustrated in Figure 12.11.
Several other variations of adaptive DM encoding have been investigated
and described in the technical literature. A particularly effective
and popular technique first proposed by [6] is called continuously variable
slope delta modulation (CVSD). In CVSD the adaptive step size parameter
may be expressed as
∆(n) =α∆(n − 1) + k 1 (12.24)
if ẽ(n), ẽ (n − 1), and ẽ(n − 2) have the same sign; otherwise
∆(n) =α∆(n − 1) + k 2 (12.25)
The parameters α, k 1 , and k 2 are selected such that 0 < α < 1 and
k 1 >k 2 > 0. For more discussion on this and other variations of adaptive
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