engines/bia-clone.js — SynthMono

The BIA Clone. Defined as a SynthEngine object with 10 modules. Models the Basimilus Iteritas Alter terrain algorithms (Basic / Bias / Bizarre) with combined decimation + wavefolding (Deci), noise injection, sub oscillator, internal Tear LFO, filter, distortion, OTT multiband compressor, compressor, and AD volume envelope.

Modules

The modules array defines both the UI panels (order, labels, params) and the signal chain (processor order).

1. OSC (source)

Param	Range	Default	Description
`waveform`	saw/triangle/sine	saw	Base oscillator waveform
`freq`	65–2000 Hz	130.81 (C3)	Oscillator frequency

The clean oscillator feeds into the terrain processing. Waveform choice significantly changes terrain character — sine gives soft harmonics, saw gives bright buzzy textures, triangle gives smooth folding in Bizarre mode.

2. Terrain (source)

Param	Range	Default	Description
`harmonics`	0–1	0.3	Morphs between three terrain algorithms
`deci`	0–1	0.15	Combined decimation + wavefolding

The terrain algorithm uses three parallel waveshaping paths, crossfaded based on the harmonics value:

Basic (harmonics 0–0.33): Sine multiplication — sin(x·π·(1 + h·3)) — generates harmonic overtones through waveshaping. Bright, clean, metallic.
Bias (harmonics ~0.5): Stepped S&H — quantises the waveform to N steps (16 down to 2). Gritty, noisy, digital.
Bizarre (harmonics 0.66–1.0): Wavefolder — multiplies the signal by 1 + h·4 and folds at ±1. Buzzy, chaotic, overdriven.

The crossfade is smooth — the three zones overlap so adjacent algorithms blend:

0      0.33    0.66     1.0
| Basic |  Bias  | Bizarre |
\        /\       /\       /
 \_____/  \_____/  \_____/

3. Noise (source)

Param	Range	Default	Description
`noiseMix`	0–1	0.3	White noise level mixed after terrain

Noise is injected after the terrain waveshapers and before the Deci stage. Unlike the BIA where noise is routed through the Bias waveshaper, this implementation mixes noise directly into the terrain sum — giving independent control and a different character.

4. Tear (source)

Param	Range	Default	Description
`tearRate`	0.1–20 Hz	3	LFO rate
`tearToHarmonics`	0–1	0	Amount of LFO → crossfade weight modulation
`tearToDeci`	0–1	0	Amount of LFO → pre-Deci gain modulation

Internal modulation LFO (sine wave) that modulates the terrain crossfade gains and/or the pre-Deci input gain. The LFO adds ±depth·0.5 to the modulated parameter, creating dynamic timbral wobble without changing the waveshaper curves themselves.

5. Filter (processor)

Param	Range	Default	Description
`filterCut`	50–20000 Hz	20000	Low-pass cutoff
`filterRes`	0–1	0	Resonance (Q: 0.5–20)

Simple cleanup low-pass filter after the Deci stage. At maximum cutoff the filter is bypassed.

6. Distortion

Standard multi-stage distortion card (same pattern as all other engines). 9 drive types, per-stage amount and drive controls.

7. Compressor (processor)

Param	Range	Default	Description
`compThreshold`	–60–0 dB	–24	Compressor threshold
`compRatio`	1–20	4	Compression ratio
`compAttack`	0.001–0.1 s	0.003	Attack time
`compRelease`	0.01–1.0 s	0.1	Release time

Standard dynamics compressor, same as other engines.

8. Volume (master)

Param	Range	Default	Description
`volAttack`	0.001–5 s	0.002	Envelope attack
`volDecay`	0.01–10 s	0.5	Envelope decay
`volSustain`	0–1	0.3	Sustain level
`volRelease`	0.01–10 s	0.3	Release time
`volume`	0–1	0.75	Master level

Extended-range ADSR envelope for percussive hits through sustained tones.

9. Normalize (builtin)

Param	Type	Default	Description
`normalize`	checkbox	true	Peak normalisation (target 0.944)

Signal Flow

OSC → Terrain (3 parallel paths crossfaded by Harmonics)
        Basic ──→ sine-multiply waveshaper ──→ ┐
        Bias  ──→ stepped S&H waveshaper  ───→ ├→ terrainSum → Pre-Deci Gain
        Bizarre → folding waveshaper      ──→ ┘
        Noise ─────────────────────────────────→┘
                                                 ↓ (tear LFO modulates if tearToDeci > 0)
                                              Deci waveshaper (decimate + fold)
                                                 ↓
                                              Filter → Distortion → Compressor → Volume → Normalize

Signal Normalisation

Unlike the kick/juno engines, this engine does not apply srcNorm normalisation — the terrain waveshapers and Deci stage inherently clip/distort the signal, making peak normalisation counter-productive. The Volume ADSR and Normalize module handle final leveling.

Rendering

getDuration returns max(1, volAttack + volDecay + volRelease + 0.1).

The render function builds three parallel waveshaper chains driven by a single oscillator, sums them with the noise path, applies the Deci waveshaper, optionally modulates with Tear LFO, and feeds the result to chainInput.

Dependencies

core.js — SAMPLE_RATE, randInRange, randInt, logRand
registry.js — register()