project name: eels
project url:
author: andrew
description: dual delay / comb filter
discussion url:
documentation url:
tags: delay looper crow arc


eels screen animated gif. two pixelated eels flop up & down in sync as 'time a' is modified. yellow backround with some random text around the sides

dual delay / comb filter with a variety of i/o modes and modulation options.

an undersea cousin of wrms.

NOTE: to view images, please read at not



also supported


install from the maiden catalog


in the maiden REPL, type:


patch notes

watch the video

read the complete patch notes

norns UI


page B of rpls, E1-3 & K2-3 are labelled

eels is split into three pages – one page for eels A & B, respectively, and an M page for setting the i/o mode & some internal modulation settings. on pages A & B, holding K1 allows you to set the modulation source for each parameter with the encoders.

available modulation sources:

note that many params use eurorack-native voltage units for pairity with crow input modulation, though eels is still designed to work well as standalone effect.

page M

page M of rpls, E1-3 & K2-3 are labelled

there are 5 i/o modes to choose from, which affect the routing of inputs & outputs, as well as the relationship between both eels.

eels has two internal LFOs, which can be set as modulation sources for parameters on the A & B pages. additional settings for each LFO are available in the params menu.

pages A & B

page A of rpls, E1-3 & K2-3 are labelled

on page B, some parameters may appear greyed-out – this means that those parameters are mapped to the value of eel A in accordance to the current i/o mode.

there are two ranges for time, which detirmines the audio effect that the eel will be set up to behave like:

the delay range can be useful for several types of effects: | range of time | use case | | — | — | | low values, -2 to 0 | looper, with feedback set high | | mid values, -1 to 3 | conventional delay | | high values, 3 to 4 | resonator, phasor, or chorus, depending on modulation & feedback settings |

the comb range turns eels into a spiky resonant filter.

the most common use for comb filters is Karplus–Strong synthesis (though eels is missing the damping lowpass filter). feed bursts of noise into the input of eels to turn it into pitched, string-like plucks. use midi or crow modulation to sequence the resonant frequency & create melodies. it can also be rewarding to feed eels a mixture of noise & musical tones, using the comb filter as a weird resonant EQ.

time is measured in volts/octave. reference the table below for the actual value of each volt (assuming fine = A and root = 440hz).

volt range = delay range = comb
-2 4.65 seconds 110 hz
-1 2.32 seconds 220 hz
0 1.16 seconds 440 hz
1 0.58 seconds 880 hz
2 0.29 seconds 1760 hz
3 0.14 seconds 3520 hz
4 0.07 seconds 7040 hz

lag sets the lag/slew value for time. set to 0 for instantaneous changes (clicky), set > 0 for smoothed encoder movements or portamento when sequencing comb filter pitch.

feedback sets the feedback level of the delay, or the decay time of the comb filter.

arc UI

arc offers high-sensitivity control of key parameters. highly reccomended!

additional params

a few more params can be accessed exclusively in the params menu:





set the modulation source for each modulatable param

lfo 1 + 2

the parameters of the internal lfos. see lib/lfo for further info.