Reverberation time is controlled by lowpass filters implemented within each feedback channel (the matrix discussed above).
A lowpass filter in series with a length delay line should approximate
, where is the ideal per-sample decay filter. In terms of a desired , this implies
Jot proposes first-order filters of the form:
where is set to give a desired reverberation time at dc and determines the reverberation time at high frequencies.
Finally, overall energy through the FDN can be equalized (to account for the effects of the loop filters) by applying a tonal correction filter at the output. For the first-order loop filters described here, a good equalization filter is given by