Cyclic modulation of amplitude in the reverb sound

[jimhen3ry]

FluidSynth version

2,2,8

Describe the bug

There is a cyclic modulation of amplitude at a rate of about once each second in the reverb sound. This is deliberate to to cancel unwanted "ringing" (resonant frequency).

Expected behavior

Add reverberation without introducing an unwanted amplitude modulation.

###Related discussion
#1139

Steps to reproduce

Add reverb to the output.

Additional context

This may be an inherent characteristic of the current reverb engine that cannot removed. The solution may be to allow the use of alternate reverb engines as proposed in #1157.