3 takes on the classic reverb design made popular by the German physicist Manford Schroeder. The basic structure is very simple, with a parallel set of feedback comb filters (sent to a mixing matrix) and a series set of all-pass filters. This particular all-pass has some specifically useful qualities for reverb reflections and is now more commonly referred to as a “diffuser”.

Patch 1: Schroeder Rvrb. Stereo reverb using classic Schroeder design with all-pass filters and feedbacking delay lines (comb filters) with tuned parameters to achieve reverb. Controls: Delay time, Filter gain, and Wet/dry mix. Stomps do nothing.

Patch 2: APF. A “supermodule” of sorts. The default all-pass is designed to be for phase shifting a la Phaser, so there is no delay time. So I made one. It’s based on the circuit in the image, using the gain coefficient as the driving factor of the patch. It’s a simpler reverb, as there’s only one feedback comb filter instead of 4, but the idea is there. Controls: Delay time, Gain coefficient, Volume. Stomps do nothing.

Patch 3: Diffuse Verb. The closest I could get to the original Schroeder design. It turns out that the Diffuser module *is* a Schroeder all-pass filter, so I basically replaced Patch 1’s all-pass section with a few of these and added some more controls for modulation and gain. Controls: Delay time, Gain coefficient, Mod width, Wet/dry mix. Left stomp is tap tempo for mod rate.

They’re all very similar but evoke a different sensation. This is not meant to be a deep, cavernous reverb, but more springy/room-esque with some feedback. Due to the all-pass not coloring the input, the frequency response has a lot of harmonics still present. Expanding on this design is what lead us to modern reverbs, so by all means, try and see what you come up with.