Machines & FM

A machine is a swappable building block inside a track. There are two kinds: the SYN machine is the synthesis engine that makes the sound, and the FLTR machine is the filter or EQ that shapes it. Each machine brings its own set of parameters, so the SYN pages and FLTR page 1 change to suit whichever machine the track is using. Any SYN machine can go on any track.

The FLTR category holds six filter machines — Multi-mode, Lowpass 4, Legacy LP/HP, Comb-, Comb+ and Equalizer. They all share an envelope and differ in their character controls; see Filter machines.

To move between a machine’s pages, use UP/DOWN, or keep pressing the same PARAMETER key to cycle round them. The screen title names the machine and the page, for example FM Tone (2/4). Hold the PARAMETER key to see the values of every parameter on the page at once. For more on editing these pages, see The SYN pages and The FLTR pages.

FM Tone is a four-operator FM synth in the classic 1980s mould, but the Digitone II uses it differently from the old FM keyboards. Rather than building the whole voice in FM, it treats the engine as a source of complex tones and passes them through a familiar subtractive chain of overdrive, filters and amp. It can still work as a complete FM voice if you want it to. If FM is new to you, start with FM synthesis basics.

Page 1 is drawn around the algorithm: the left of the screen shows how the operators are connected and which ones feed the X and Y outputs, and FDBK acts on the operator drawn with a feedback loop. FM harmonics includes a chart of which part of the engine each page 1 parameter touches.

Frequency modulation means using one oscillator’s output to wobble another oscillator’s pitch. Do it slowly and you get plain vibrato, as with an LFO. Push the modulating oscillator up to audio rate and the wobble stops sounding like vibrato and becomes part of the tone itself, adding new harmonics.

The Digitone II’s twist is what happens next. The FM Tone engine produces the raw, often complex FM tone, and then the sound passes through overdrive, the base-width filter, the filter machine and the amp, just as on a subtractive synth. You get FM’s timbres with filter-and-envelope shaping you may already know.

The manual illustrates the basic idea with a carrier at ratio 1 and a modulator at ratio 8: the output keeps the carrier’s slow cycle, but with the modulator’s fast ripples written into its shape.

Operator groups. To keep things manageable, the four operators are arranged in three groups: C, A and B, where B is a pair, B1 and B2. Controls for group B are macro-mapped, so one knob sets both B operators at once — see RATIO B in FM ratios and detune and LEV (B) in FM operator envelopes.

An algorithm is a fixed way of wiring the four operators together. Changing it changes how the modulation is applied, and the sound can change dramatically — stacking all four operators, each modulating the next, can produce very complex timbres. Choose one with ALGO on SYN page 1 of the FM Tone machine; the screen draws the current routing.

Outputs not marked “envelope-shaped” are drawn with dotted lines in the manual, so they leave at their own level. Several algorithms use an operator in both roles: in 1 and 4, B1 modulates another operator and is heard at Y; in 5 and 7, A modulates C while also reaching an output.

In FM, each operator runs at a multiple of the note you play rather than at a pitch of its own. That multiplier is the ratio, and the higher the ratio, the higher the operator’s frequency. Working in multiples of the note is what keeps an FM sound tonal.

Fine-tuning ratios. SYN page 4 has a RATIO OFFSET for each of the four operators — C, A, B1 and B2 — which nudges that operator’s ratio away from the value set on page 1. DTUN on page 1 detunes operators A and B2 by offsetting their ratios: the effect stays very slight up to a value of about 64, good for gentle movement, and gets much stronger above that.

Key tracking. Also on page 4, KEY TRACK A, KEY TRACK B1 and KEY TRACK B2 reduce an operator’s modulation as you play higher up the keyboard. At 0 the modulation is the same on every note; higher settings thin it out more and more towards the top. Less modulation means a simpler tone, so high notes come out less complex — much as many acoustic instruments behave.

All four ratio offsets and the key tracking controls are on SYN page 4 — see the page in FM Tone machine.

Letting one operator modulate another at full strength gives very harsh harmonics, so the Digitone II tames the modulation in two ways: a level control sets how much there is, and an envelope moves it over time. That movement is what makes FM sounds come alive — think of a piano, whose tone is bright at the moment of the strike and quickly mellows. On FM Tone, the envelopes and levels are your main sound-shaping tools.

How LEV (B) drives two operators. Because group B is a pair, one LEV (B) knob sets the modulation from both B1 and B2 along a fixed curve:

The envelope and level controls are on SYN pages 2 and 3 of FM Tone machine.

Every operator starts out as a sine wave. HARM on SYN page 1 adds upper partials to some of them, giving the FM engine richer raw material to work with. The knob is bipolar: turn it below zero to change operator C, above zero to change operators A and B1. Its range is -26.00 to 26.00.

Values between two steps blend the neighbouring harmonic settings, much like moving through a wavetable, so sweeping HARM glides smoothly from one timbre to the next.

How the waveforms are made. The series is built with a form of additive synthesis: adding sine waves, called partials, at different volumes to build up a more complex wave. The first partial always stays at full volume, which keeps the base octave intact. Add every partial, each a little quieter than the one before, and you get a sawtooth; add only the odd ones and you approach a square wave; other mixes give other sounds, such as something close to a bell.

FM Drum is an FM engine shaped for drums and other percussion, though it handles melodic sounds well too. Each hit is built from three parts you can balance: a body made by three FM operators, a noise layer and a transient. A wavefolder works on the body alone, while noise and transient share a filter and an envelope.

STIM and SDEP set the pitch sweep — lower STIM values make the sweep shorter. FOLD only folds the body, never the noise or transient, adding overtones as you turn it up. On the algorithm drawing for this machine, the operator with feedback carries a loop at its upper right.

Wavetone is a two-oscillator engine built for shaping waveforms. It borrows from several synthesis styles — phase distortion, wavetables, ring modulation and hard sync — and adds a flexible noise generator with its own envelope. Page 1 sets up the two oscillators, page 2 holds their wavetables and offsets and decides how they interact, and page 3 is the noise.

Linear offsets. OFS1 and OFS2 detune each oscillator by a fixed number of hertz, rather than in cents as TUN1 and TUN2 do. A fixed offset is more noticeable on low notes than high ones, and the beating between the oscillators stays at the same speed whatever note you play — a different kind of chorus-like detune. DRIF adds random pitch drift to both oscillators.

Swarmer builds a big sound from one main oscillator and a swarm of six extra oscillators detuned around it. Everything fits on a single SYN page: pick waveforms for the main oscillator and the swarm, set how far the swarm spreads and how loud it is, then bring it to life with animation and noise modulation.

FLTR page 1 belongs to the track’s filter machine. All six machines share the same frame — an envelope on the top row (ATK, DEC, SUS, REL), the frequency on E and the envelope depth ENV on H — and differ in the one or two controls in between that give each its character. FLTR page 2 holds the base-width filter and more envelope settings (The FLTR pages).

Multi-mode changes type with one knob: turn TYPE to morph from low-pass through band-pass to high-pass. RESO adds a resonant peak at the cutoff.

Lowpass 4 is a four-pole low-pass filter with a 24 dB/octave slope, steeper than the 12 dB/octave of Legacy LP/HP. There is nothing on G.

Legacy LP/HP takes its inspiration from the filter on the original Digitone. TYPE switches it between low-pass and high-pass, both with a 2-pole, 12 dB/octave slope.

Comb- and Comb+ are comb filters. They add metallic, resonant overtones tuned to a pitch: FREQ tunes the resonances, FDBK sets the gain of the feedback signal and LPF sets a low-pass filter inside the feedback path. The difference is the sign of the feedback. Comb- feeds back negatively for a hollow, tube-like sound; Comb+ feeds back positively for something more like a string.

Equalizer is a parametric EQ rather than a filter: use it to lift frequencies you want more of or cut ones you don’t. FREQ sets the centre frequency, GAIN the boost or cut around it and Q the width of the band — the higher the Q, the narrower the band.