Two-Filter Component-Modelled Monosynth

Scheele Green

Louder is a different sound.

Scheele Green is a monosynth built on two filters that do opposite things when you hit them harder. The first is tuned by diodes, and a diode conducts more the more voltage you put across it: drive it and it opens up and tears. The second is built from logic chips pressed into service as amplifiers, and their gain falls away toward the rails: drive it and it blunts, fizzes, and its resonance sags. One feeds the other. There is a knob for how hard you hit each. And your velocity arrives before both of them, so a hard note is not a louder copy of a soft one. It is a different sound.

The engine underneath

VST3 · Windows 64-bit·No activationmacOS VST3 and Audio Unit are in development.

The Scheele Green front panel: deep forest-green steel with brass section tabs and walnut cheeks. Top left, an oxblood nameplate reading SCHEELE GREEN, TWO FILTERS. OPPOSITE MANNERS. ONE VOICE. Beside it a phosphor readout showing 13 - REVOLVING DOOR over LOUDER IS A DIFFERENT SOUND, then GATE and ACCENT lamps, an output meter and a POWERED BY PHONON badge. The top row holds VCO 1, VCO 2 and VCO 3, each with TUNE, WAVE and PW knobs and an OCTAVE window; a SOURCES box with noise colour and sub; then THE GRID - SIX SOURCES, THREE WAYS IN: three rows labelled LP IN, BP IN and HP IN, each with six small knobs under the headings VCO 1, VCO 2, VCO 3, SUB, NOISE and RING, and a lit meter at the end of each row, with the line ALL THREE ARE LIVE AT ONCE UNDER ONE RESONANCE printed beneath. To its right, PUSH - THE DIODE FILTER with PUSH, CUTOFF, RESO, ENV 2 and KEY knobs and the line LOUDER OPENS AND TEARS, and LOAD - THE CMOS FILTER with LOAD, CUTOFF, RESO, a MODE window reading LOW, ENV 2 and KEY, and the line LOUDER BLUNTS AND FIZZES. The middle row holds ENV 1 AMP, ENV 2 FILTERS and ENV 3 as slider banks with RC and LINEAR CIRCUIT switches, two LFO panels, THE HAND with GLIDE, VEL TO LEVEL and ACCENT, and an OUTPUT box with DRIVE and VOLUME. Below them an eight-slot MODULATION MATRIX whose first two rows read LFO 1 to BP IN and LFO 1 to LP IN, then CHORUS, ECHO and SPRING boxes and a green SCOPE holding a waveform, with PUSH and LOAD bars under it. Along the bottom, THE PLAYER - AN ARPEGGIATOR OR SIXTEEN STEPS FROM THE KEY YOU HOLD: MODE, RATE, arpeggiator-order and OCTAVES windows, GATE, SWING, LENGTH and SLIDE knobs, and sixteen numbered steps showing offsets like 0, +12, +3 and +7 with SLD and ACC buttons under each.

“It’s loud.”

Meadow, founder, Aphelion

Six sources, three ways in

The mixer is the filter

Most synths have a mixer, then a filter with a mode switch. This has neither. The diode filter needs no mode switch because it has a lowpass input, a band-pass input and a highpass input, and all three are live at once - so the mixer is those three inputs. Six sources across, three ways in down the side, a knob at every crossing and a meter on every input.

Send a saw in at the lowpass while a square an octave up goes in at the highpass and the sub goes in at the band-pass: one filter, one cutoff, one resonance, three different things happening to three different sounds.

The lowpass door. The fundamental stands over the 30th harmonic by a distance you could park a bus in.

+45.0dB, the fundamental against the 30th harmonic

One saw, one corner at 1.5 kHz, played gently, sent in at each door in turn. Same filter, same resonance - and through the highpass the note is under its own thirtieth harmonic.

THE GRID - SIX SOURCES, THREE WAYS IN: three rows of six small knobs labelled LP IN, BP IN and HP IN, under column headings VCO 1, VCO 2, VCO 3, SUB, NOISE and RING, each row ending in a lit meter reading a different level. Underneath, the line ALL THREE ARE LIVE AT ONCE UNDER ONE RESONANCE. To the right, the PUSH box headed THE DIODE FILTER with the line LOUDER OPENS AND TEARS, and the LOAD box headed THE CMOS FILTER with the line LOUDER BLUNTS AND FIZZES.

With the sub into LP IN and a saw two octaves above it into HP IN at the same time, the sub's 110 Hz reads -14.4 dBFS while the saw's own 440 Hz fundamental is down at -43.3 and its 3.5 kHz at -41.2. The filter kept the bottom of one and the top of the other.

The same knob, twice

Two filters, opposite manners

PUSH and LOAD are the level going into each filter, taken back out again afterwards - most of the way - so they are tone controls rather than volume controls. The two circuits answer that gesture in opposite directions, which is the whole instrument.

PUSH

The diode filter

Louder opens, and tears

Its tuning elements are diodes, and a diode conducts more the more voltage you put across it - so every loud moment in the wave briefly opens the filter.

36.9dB under the fundamental

Tearing. The diodes are opening on every loud moment in the wave.

A saw at A2 through a 500 Hz corner: where its 30th harmonic sits. 25.3 dB between the ends of the knob, while the output level moves 5.0 dB.

LOAD

The CMOS filter

Louder blunts, and fizzes

Its amplifiers are logic inverters biased into their linear region and asked to be op-amps. They are not good at it, and their gain falls away toward the rails.

22.3dB under the fundamental

The filter has given up: the harmonic is now further down than a plain saw would leave it.

At full resonance, with the corner sitting on a saw's 8th harmonic. 21.7 dB between the ends of the knob, where a plain saw's 8th harmonic sits 18 dB under. So at LOAD 5 the resonance is lifting that harmonic 17.4 dB above where a plain saw leaves it, and at LOAD 100 the filter is taking 4.3 dB off it.

One stranger thing

The door that rebuilds what it filtered

Put a sound in at the highpass, where its fundamental is filtered away, and then drive it. The diodes rebuild the missing fundamental out of the harmonics that are left - so the note comes back out of a door that had just removed it.

And with the keyboard on its corner, the first filter sings on its own and plays well enough to be the oscillator.

The fundamental, against its 30th

Through HP IN

-11.3 dB

Under its own 30th harmonic.

The same note at PUSH 80

+11 dB

Over it. The diodes put back 22.3 dB of a fundamental the filter had taken out.

Singing on its own, C4 and C5

302.8 · 605.8 Hz

Sharp of the corner, and an octave apart to within 0.6 of a cent.

Before both filters, not after

A hard note is a different sound

Velocity and ACCENT are level before both filters. Play softly and both circuits stay in their linear manners; dig in and the first one opens while the second one chokes. Measured with the envelope taken out of it and PUSH at 80, on the 30th harmonic:

At velocity 20, the 30th harmonic sits59.9 dB under

At velocity 10044.8 dB under

Which is, from your fingers alone15.1 dB of brightness

A legato octave with GLIDE at 200 ms, fifty milliseconds in161 Hz

And at the end of it219 Hz

DUO, holding C3 and E4: two keys, two pitches, one filter path130.4 · 329.6 Hz

GLIDE is a capacitor, so it starts fast and lands slowly. DUO is duophonic - two keys through the one filter path - which is a different thing from a second voice, and this instrument does not have one.

What goes in

Three oscillators, and a logic gate

Each is a saw core behind a real exponential converter, with a wave knob that sweeps sine through triangle and saw to pulse. The second syncs to the first. The third can frequency-modulate the first through zero - or flip its CORE switch and become something else entirely: a Schmitt-trigger oscillator, a logic gate charging a capacitor, the rawest square there is. Beside them a sub that is a real divider off the first oscillator's core, so it cannot drift against it; noise from white to pink; and a ring modulator made of four unmatched diodes.

A4 plays at438.29 Hz

A2109.83 Hz

Which is, as the parts were drawna fifth of a per cent flat

Two fresh copies of the instrumentdiffer by nothing, sample for sample

The oscillators' parts have tolerances, and they are the same tolerances every time you open it.

Eight slots, and three doors

The matrix can open a door

Three envelopes, each switchable between RC and constant-current. Two LFOs with tempo sync, delay and key reset. And an eight-slot matrix of source, VIA, destination and amount - where the destinations include the grid's three columns. An LFO can fade the band-pass input up while it fades the lowpass input down. An envelope can let a note's attack in through one door and its body through another.

Measured: an envelope on HP IN through the matrix takes a note that came in at the highpass from -34.0 dBFS to under -140. The door shuts.

The MODULATION MATRIX box: eight numbered rows in two columns, each with a SOURCE window, a VIA window, a DESTINATION window and an AMOUNT knob. The first row reads LFO 1 into BP IN and the second LFO 1 into LP IN; the rest are set to NONE with a destination of CUTOFF 1.

Sixteen steps from the key you hold

The player

Off, an arpeggiator, or a line. The arpeggiator goes up, down, up and down, as played, or by dice, over one to three octaves. The line is sixteen steps of offsets from whatever key you hold: each step a note or a rest, with a slide and an accent. A slide is the glide capacitor with the line's own resistor. An accent is more level into both filters - which by now you know is not the same as louder.

The line as it ships, on one held key at 12024 notes in two bars

Under the host's clock, at bar 1 and at bar 3on step 1 both times

An accented step, against its neighbour-10.9 against -16.1 dBFS

A slide up an octave, fifteen milliseconds in165 Hz

And by ninety213 Hz

THE PLAYER - AN ARPEGGIATOR OR SIXTEEN STEPS FROM THE KEY YOU HOLD: MODE, RATE, arpeggiator-order and OCTAVES windows beside GATE, SWING, LENGTH and SLIDE knobs, then sixteen numbered steps showing offsets - 0, a rest, 0, +12, a rest, 0, +3, 0, 0, a rest, +12, 0, a rest, +7, +5, 0 - each with SLD and ACC buttons beneath, several of them lit. Underneath, the line DRAG A STEP FOR ITS NOTE - DOUBLE-CLICK RESTS IT - A SLIDE TIES IT TO THE NEXT - AN ACCENT HITS BOTH FILTERS HARDER.

With the host running the line sits where the song says, so a bounce is the playback; with the host stopped it runs free from the key. The line is saved with your session.

Demos

14 takes, played by us

Straight out of the plugin, no processing on the way here, levels matched so you can move between them without reaching for the volume.

Take 01

Take 02

Take 03

Take 04

Take 05

Take 06

Take 07

Take 08

Take 09

Take 10

Take 11

Take 12

Take 13

Take 14

The sheet

What is in the box

Everything nonlinear in the voice runs at twice the sample rate, and both filters are solved implicitly, every sample, as circuits. On the machine it was timed on it runs about twelve times faster than realtime with all three effects in - that is one machine, and not a promise about yours.

FormatVST3 instrument · Windows 64-bit

In developmentmacOS VST3 and Audio Unit

VoiceMonophonic · last-note priority · legato or retrigger

DuoTwo keys, two pitches, one filter path

Sources3 oscillators, divider sub, noise, diode ring modulator

The grid6 sources × 3 filter inputs, all live at once

First filterDiode-tuned, three inputs, self-oscillating and tracking

Second filterCMOS-inverter state-variable: low, band, high, notch

Push25 dB of brightness out of a level knob, 5.0 dB of level

LoadResonance that sags instead of singing

The hand15 dB of brightness between velocity 20 and 100

Envelopes3 · RC or constant-current · loop on the third

Matrix8 slots · 14 sources, 27 destinations, VIA on each

PlayerArpeggiator, or 16 steps with rest, slide and accent

After the filtersClass-A drive, chorus, tape echo, spring tank

Controls134 · 16 presets · phosphor readout and scope

The panel1520 by 976

Measured31 claims · validator 47 of 47

InstancesSample-identical, two fresh copies

ActivationNone. No license server, no phone-home

EngineTwo new circuits in Phonon: both filters

A green too good to be safe

In 1775 a chemist made a green so vivid that everyone put it on their walls, and it was made of arsenic. We liked the name. Both filters here are new circuits in the Phonon engine, written for this instrument; everything around them is Phonon's shelf. It is the monosynth beside Tyrian Blue's polysynth.

The rest of the shelf

VST3 · Windows 64-bit - macOS VST3 and Audio Unit are in development. No activation, and the plugin never asks who you are.

At a glance

Scheele Green specifications

Technical specifications for Scheele Green, Two-Filter Component-Modelled Monosynth
Format	VST3 instrument · Windows 64-bit
In development	macOS VST3 and Audio Unit
Voice	Monophonic · last-note priority · legato or retrigger
Duo	Two keys, two pitches, one filter path
Sources	3 oscillators, divider sub, noise, diode ring modulator
The grid	6 sources × 3 filter inputs, all live at once
First filter	Diode-tuned, three inputs, self-oscillating and tracking
Second filter	CMOS-inverter state-variable: low, band, high, notch
Push	25 dB of brightness out of a level knob, 5.0 dB of level
Load	Resonance that sags instead of singing
The hand	15 dB of brightness between velocity 20 and 100
Envelopes	3 · RC or constant-current · loop on the third
Matrix	8 slots · 14 sources, 27 destinations, VIA on each
Player	Arpeggiator, or 16 steps with rest, slide and accent
After the filters	Class-A drive, chorus, tape echo, spring tank
Controls	134 · 16 presets · phosphor readout and scope
The panel	1520 by 976
Measured	31 claims · validator 47 of 47
Instances	Sample-identical, two fresh copies
Activation	None. No license server, no phone-home
Engine	Two new circuits in Phonon: both filters