Norns: what is the reverb algorithm? [SOLVED]

SimonKirby · 2020-03-12T11:21:21.881Z

This is really not a very important question - just curiosity! I was comparing the reverb in Norns to the one in Clouds (which I love and has been my go-to end of chain eurorack reverb for a while) and they are remarkably alike to my ears. This makes me happy, and one step closer to a plan to downsize my eurorack to a palette case, (which seems to be what all the cool kids are doing these days).

However it also made me idly wonder if norns and clouds use the same algorithm? Or if my ears are just completely worn out and everything sounds equally lovely

jah · 2020-03-12T12:41:48.850Z

AFAIK it’s generated using Faust based on an algorithm called Zita: https://github.com/monome/norns/blob/master/crone/src/effects/ZitaReverb.h

@catfact may have more details

PaulBatchelor · 2020-03-12T14:18:52.929Z

The FAUST implementation was written by Julius Smith. The algorithm and original implementation (zita-rev1) was written by Fons Adriaensen:

https://ccrma.stanford.edu/~jos/pasp/Zita_Rev1.html

https://faust.grame.fr/doc/libraries/index.html#re.zita_rev1_stereo

For reference, here is the Clouds Reverb algorithm implementation:

github.com

pichenettes/eurorack/blob/master/clouds/dsp/fx/reverb.h

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From a pure technical and non-perceptual perspective, the algorithms do technically differ quite a bit. Zita is a higher-order FDN system that makes formal use of a feedback matrix. Clouds reverb, from what I’ve seen looks closer to a classic schroeder design with LFO modulation, similar to what was described in that famous dattorro paper (a very popular reverb design). The LFO-controlled modulation makes it sound like a denser higher-order, and it also smooths out some of the ringiness you often get with schroeder-reverb designs.

toneburst · 2020-03-12T15:15:52.101Z

One of the primary drivers of the reverb implementation in Clouds was the necessity to make it work alongside all the other stuff that was going on, within the limited resources of the Clouds’ Cortex M4 processor.

If it sounds good, it’s testament to @pichenettes skill in optimising for very limited processor resources.

SimonKirby · 2020-03-12T18:27:12.435Z

toneburst:

If it sounds good, it’s testament to @pichenettes skill in optimising for very limited processor resources.

It really does, and her skills are legendary!