EELS

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 github.com not norns.community

hardware

required

• norns (220321 or later)

also supported

• crow
• arc

install

install from the maiden catalog

or

in the maiden REPL, type:

;install https://github.com/andr-ew/eels/releases/download/latest/complete-source-code.zip

patch notes

watch the video

read the complete patch notes

norns UI

intro

• K2: increment page
• K1 (hold): set modulation source

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:

• lfo 1: internal LFO.
• lfo 2: internal LFO.
• crow in 1 & crow in 2: control voltage from crow. time tracks v/oct, levels expect 0-5v.
• midi: midi note value, converted to volt/octave.
• clock: an offset that will sync time = 0 with the global clock tempo in delay mode. positive whole number voltages will be multiples of the clock, negative whole number voltages will be divisions of the clock.

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

• E1: i/o mode
• E2: internal lfo period
• E3: internal lfo depth
• K3: lfo focus 1/2

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

• coupled: all B controls are coupled with A, but time b is the sum of the A & B voltage values.
• decoupled: separate A & B controls.
• series: decoupled controls, A delay routed into B.
• ping-pong: all B controls coupled with A, ping-pong feedback between delays.
• send/return: A delay only (left channel), external feedback loop (right channel).
  • input L: dry signal, patch from input or mixer send
  • output L: wet signal, patch to mixer
  • output R: patch to the input of external effect (such as a filter)
  • input R: patch in from the output of external effect
  • for best results, be sure to silence the system monitor level.

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

• E1: delay time (v/oct)
• E2: delay time slew/lag (volts, 0 to +5)
• E3: delay feedback (volts, -5 to +5)
• K3: delay range

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:

• delay: 4.65s - 0.07s
• comb: 110hz - 7040hz

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.

• time now sets the resonant frequency of the filter
• feedback sets the resonance/decay time of the spectral spikes

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).

• NOTE: the range is quite wide - when mapping to a midi controller, you may want to reduce the output range of the mapping for more sensitive control.
• NOTE: in comb range, ping-pong & send/return modes do not track v/oct correctly

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!

• time a
• feedback a
• time b
• feedback b

additional params

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

modes

• input: mono or stereo audio input. only effects coupled, decoupled, and series modes.

time

• time a quant & time b quant
  • free: continuous control over time.
  • oct: time is quantized to whole numbers. this has different use cases in each range.
    • comb range: time becomes an octave control
    • delay range w/ clock modulation: time becomes a clock multiplier/divider. reference the table for multiple/division at each volt: | volt | time in beats | | —— | ——————- | | -2 | 4 | | -1 | 2 | | 0 | 1 | | 1 | 1/2 | | 2 | 1/4 | | 3 | 1/8 | | 4 | 1/16 |
• fine: fine tune the time value in semitones. adjusts the musical key when sequencing the comb filter pitch via crow. no need to adjust when sequencing over midi.
• root: set the concert pitch frequency for time.

levels

• input a & input b: audio input level
• output a & output b: audio output level
• stereo width: set the output stereo separation between A & B.

modulation

set the modulation source for each modulatable param

lfo 1 + 2

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

pset

• reset all params: resets all params to default values
• overwrite default pset: when autosave is disabled, sets the current state as the default state when starting the script.
• autosave pset: disables saving the pset to the default slot when exiting the script. when enabled, settings will persist between sessions.