Following Schroeder's original insight, the delay line lengths in an
FDN (
in Fig.3.10) are typically chosen to be mutually
prime. That is, their prime factorizations contain no common
factors. This rule maximizes the number of samples that the lossless
reverberator prototype must be run before the impulse response
repeats.
The delay lengths
should be chosen to ensure a
sufficiently high mode density in all frequency bands. An
insufficient mode density can be heard as ``ringing tones'' or an
uneven amplitude modulation in the late reverberation impulse
response.