### Equivalence of Parallel Combs to TDLs

It is easy to show that the TDL of Fig.2.19 is equivalent to a
*parallel combination* of three feedforward comb filters, each as in
Fig.2.23. To see this, we simply add the three comb-filter transfer
functions of Eq.(2.3) and equate coefficients:

which implies

We see that parallel comb filters require *more delay memory*
(
elements) than the corresponding TDL, which only
requires
elements.

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Filtered-Feedback Comb Filters