Chapter 02: Synthesis Engine & Layer Morphing

2.1 Dual Layer Architecture (Layers A & B) and Morphing

The core of TOMiC's sound engine is built around the Dual Layer Architecture. Each of the 16 instrument channels contains two complete, independent synthesizer instances: Layer A and Layer B (defined as ChannelParams::a and ChannelParams::b — both full instances of VoiceParams).

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Morph Control Panel

Figure 2.1: Real-time Morphing control panel blending between Layer A and Layer B.

How Layer Morphing Works

The global Morph control continuously interpolates and blends multi-parameter DSP states between layers:

2.2 Synthesis Types (SynthesisType)

Each oscillator (OSC1 and OSC2) within each layer (A/B) can operate in one of 12 synthesis architectures (SynthesisType):

The GUI splits carrier selection across two dropdowns: Type picks the architecture (Wave/Mesh/FM/Ring/Cluster/Harmonics/Ring+Braids/Plaits/FM+Braids/FM+Plaits), while the unified Wave dropdown picks the actual sound source — a standard waveform, one of the 42 Braids algorithms, or one of the 9 Plaits engines — depending on which architecture is active. Picking a Braids or Plaits entry from Wave automatically swaps the Type to the matching Braids/Plaits carrier while preserving whichever FM/Ring architecture was already selected (e.g. picking a Braids wave while in FM stays FM+Braids rather than resetting to plain Braids).

An FM Engine switch (FmEngine: Linear / Phase) changes how the modulator affects the carrier for all FM-family architectures: Linear adds the modulator directly to the carrier's frequency each sample (TOMiC's original behavior); Phase adds it to the carrier's phase for textbook Chowning/DX7-style FM sidebands. Braids/Plaits FM carriers only honor Phase mode for the subset of algorithms/engines that have a genuine phase concept (most of them — see 2.4/2.5); the rest silently fall back to Linear.

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Synthesizer Oscillator Section

Figure 2.2: Oscillator and sound synthesis section interface.

2.3 Oscillator Waveforms (Wave Mode)

In Wave mode, the following waveforms are available (Waveform enum):

2.4 Braids Macro Oscillator

TOMiC includes an integrated macro oscillator engine derived from the eurorack module Mutable Instruments Braids. Available algorithms (BraidsWave, 42 total, listed in code/discriminant order):

Each algorithm exposes 3 modulatable macro controls — Timbre, Color, Aux — but their meaning is remapped per algorithm (e.g. for AnalogBd, Timbre is tone/click amount, Color is decay length, Aux is pitch-drop depth; for Vowel, Timbre/Color/Aux sweep vowel position, formant shift and nasality). Hover any knob in the editor for a per-algorithm tooltip. Aux is always centred at 0.5 (the neutral/classic sound) rather than at 0.

Braids can be combined with other architectures from the Type dropdown: plain Braids (via Wave), Ring+Braids (ring-modulated), and FM+Braids (Braids as an FM carrier, frequency-input only).

2.5 Plaits Macro Oscillator

Alongside Braids, TOMiC ships a second, independently-ported macro-oscillator family: a clone of Mutable Instruments Plaits (dsp/plaits_osc), built fresh from Plaits' own DSP rather than reusing Braids code, so it contributes genuinely different sound categories. The first pass ships 9 engines (PlaitsModel):

Plaits reuses the same three macro knobs as Braids, remapped as Harmonics (onto the timbre param), Timbre (onto color), and Morphology (onto aux) — the labels differ per engine (e.g. for AnalogBassDrum: Harmonics = attack sharpness, Timbre = pitch drop depth, Morphology = decay time).

Plaits can be combined with FM (FM+Plaits, Plaits as the FM carrier) but not with Ring or the Granular carrier slot. It is not available while Granular, Ring+Braids or FM+Braids are active, since those are Braids-carrier-only modes.

2.6 Granular Processor (CloudsProcessor)

TOMiC utilizes a port of the Mutable Instruments Clouds engine with 5 granular processor instances:

The oscillator granular layer is enabled per-oscillator via the universal Granulate checkbox (gran_layer_enabled), which layers the grain cloud on top of whatever synthesis architecture is active rather than replacing it — this is what superseded the old dedicated Granular SynthesisType.

Active Granular Controls

Older Grain Scatter, the pre-Clouds Grain Density/Grain Window pair, and Grain Reverse are legacy parameters kept only so older DAW sessions still recall correctly — they are no longer read by the audio engine.

2.7 Cluster Oscillator

The Cluster architecture (ClusterOscillator) generates a bank of 2–6 detuned partials (Cluster Cnt, default 6) for dense chords and bell-like harmonic structures:

2.8 Harmonics Oscillator

The Harmonics architecture (HarmonicOsc) is a Tremor-inspired additive oscillator with two operating modes (HarmonicsMode: Membrane default, or Harmonic) and a selectable per-partial waveform (HarmonicsWave: Sine, Triangle, Square, or Sawtooth):

2.9 Per-Voice Signal Topology

Beyond the oscillator/noise carriers, each Layer (VoiceParams) exposes a small set of controls that shape how its signal is routed and combined:

2.10 Mesh 2D FDTD Plate Physical Modeling Oscillator

TOMiC features a real-time 2D Finite-Difference Time-Domain (FDTD) biharmonic acoustic plate solver on both OSC 1 and OSC 2 across Layer A and Layer B. Unlike static sample libraries or modal resonators summing fixed sine banks, Mesh 2D physically simulates the transverse wave propagation, mechanical stiffness dispersion, boundary reflections, and natural structural damping of a physical struck plate in real time.

Mathematical Solver & Real-Time Stability

$$2S + 16K + 4D_1 \le 1$$

where $S$ is the wave propagation/tension coefficient, $K$ is the biharmonic stiffness/dispersion factor, and $D_1$ is damping. This mathematical constraint guarantees zero risk of numerical explosions or DC runaway across all parameter ranges, requiring zero dynamic memory allocation on the real-time audio thread.

5 Boundary Geometry Masks

The boundary of the active plate grid can be shaped into 5 physical geometry masks, each exhibiting distinct acoustic eigenmodes:

1. Circle: Classic cymbal, gong, or bell geometry with concentric Bessel vibration nodes.

2. Square: Orthogonal reflection geometry producing chime-bar and metallic plate tones.

3. Ellipse: Asymmetric boundary introducing subtle modal splitting, acoustic beating, and shimmering flutter decay.

4. Hexagon: Complex multi-axial reflections suited for raw industrial hits and metallic snares.

5. Chladni: A disc pinned on the antinodes of a seeded plane-wave interference field (about 8 % of the area), with a pin-free core so the lowest mode always sits where the stick lands. Every seed yields a different set of pins — and a different modal fingerprint — without ever cutting the plate into silent islands; the strike point and pickups snap to solid material so no seed reads a hole edge.

Every shape is tuned to its real lowest eigenmode (solved on the built mask whenever the geometry, size or seed changes) rather than to an idealised pinned square, so a rimmed circle or hexagon lands on the note the Tune knob says. Rim-only changes are scaled analytically and never clear a ringing grid — an LFO on Rim no longer wipes the previous hit at every strike.

Dynamic Re-Strike Interference (Zero Machine-Gun Repetition)

In standard sample-based or static wavetable synthesizers, rapid successive hits either abruptly restart the sound or trigger independent parallel voices that sound identically repetitious. In Mesh 2D, the physical displacement and velocity state of the plate grid persists across voice triggers. Subsequent strikes land on a plate that is already vibrating. Wavefronts physically collide, cancel, and reinforce in real time. Rapid 16th-note rolls naturally build acoustic turbulence and organic sonic evolution, eradicating the artificial "machine-gun" effect completely without needing multi-gigabyte round-robin sample folders.

Physical Choke & Dampening

Hi-Hat choke and voice choke groups in Mesh 2D do not simply clamp an amplitude envelope. Instead, choke dynamically injects heavy numerical damping directly into active grid cells — exactly like a percussionist dampening a ringing cymbal or gong with a hand. Subsequent strikes automatically lift the damping.

Real-Time 16×16 Modal Vibration Heatmap

A normalized 16×16 modal visualizer rendered above the preset bar displays active surface deformations and nodal lines while the plate vibrates. The visualizer is published only when the plate is active, maintaining idle overhead at less than ~7ns per audio block.

Mesh 2D Parameters & Modulation

2.11 Hosted Instrument Plugins (Standalone Only)

In Standalone mode, a channel layer's own sound source can be replaced by an external plugin instead of TOMiC's internal engines — turning the whole modulation matrix, sequencer and macro system into a generative brain for a third-party synth.

Hosting an effect plugin (rather than an instrument) on a channel or the Master bus is a separate feature — see 5.15 In-Process CLAP FX Hosting.

2.12 Melodic, Bass & Harmonic Sound Design in the Groovebox

While TOMiC originated around raw percussive physics, v0.6 is engineered as a complete Groovebox workstation capable of handling every tonal and harmonic duty in your arrangement:

Combined with scale-quantized pitch sequencing (see Chapter 06), each of TOMiC's 16 channels can fluidly alternate between rhythm, bass, melody, and harmonic accompaniment.