### Feedback Comb Filter Amplitude Response

Figure 2.26 shows a family of *feedback*-comb-filter
amplitude responses, obtained using a selection of feedback
coefficients.

Figure 2.27 shows a similar family obtained using
*negated* feedback coefficients; the opposite sign of the feedback
exchanges the peaks and valleys in the amplitude response.

As introduced in §2.6.2 above, a class of feedback comb filters can be defined as any difference equation of the form

*z*transform of both sides and solving for , the transfer function of the feedback comb filter is found to be

so that the amplitude response is

*sign-inverted*.

For , the feedback-comb amplitude response reduces to

Note that produces resonant peaks at

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Filtered-Feedback Comb Filters

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Feedforward Comb Filter Amplitude Response