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Multi-Phasor Gate and trigger decision

The Multi-Phasor Gate (MultiPhasorGateInternal in private/src/MultiPhasorGate.hpp) decides, per voice, whether to emit a trigger – the gate that starts a note and drives the AHD envelope and the rest of the voice chain. The Nonagon feeds it from the Theory of Time, LameJuis, and index arp, then the Multi-Phasor Gate combines phasor-based gate timing with trigger logic so that only one condition (or the right combination) actually fires a note.

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Overview

• There are 9 voices (3 trios of 3). Each voice has a gate (m_gate[i]) and an AHD control (m_ahdControl[i]). The downstream synth uses m_ahdControl[i].m_trig as “this voice should start a note this frame.”
• The trigger decision is split into:
  1. Trigger logic (NonagonTrigLogic) – Builds a boolean m_trigs[i] and m_newTrigCanStart[i] per voice from LameJuis triggers, index-arp “triggered,” mutes, and interrupt rules.
  2. Multi-Phasor Gate Process – Combines those with phasor-based timing and mute to set m_ahdControl[i].m_trig and m_gate[i], and to turn the gate off after half a voice-period.

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1. Inputs to the trigger logic

The Nonagon sets these before calling SetInput (in SetMultiPhasorGateInputs):

• m_running – From input.m_running (transport running). Must be true for any new trigger to be allowed.
• m_pitchChanged[i] – True when the Theory of Time had a change this frame and LameJuis output for that voice raised a “pitch changed” trigger (m_lameJuis.m_lanes[trio].m_trigger[voiceInTrio]).
• m_subTrigger[i] – True when the index arp for that voice m_triggered this frame and the Theory of Time had a change.
• m_earlyMuted[i] – Reserved for future mute logic; currently always false. Used to block triggers and “new trig can start” when true.
• m_mute[i] – Per-voice mute from the UI (stored in trig logic state).
• m_trigOnPitchChanged[trioId], m_trigOnSubTrigger[trioId] – Per-trio: whether to fire on “pitch changed” and/or on “sub-trigger” (index arp triggered). Defaults: pitch-changed on, sub-trigger off.
• m_interrupt[trioId][jTrioId] – If true, a trigger on a voice in trio j can interrupt (cancel) a trigger on a voice in trio i when voice i has a higher index than voice j.
• m_unisonMaster[trioId] – For unison: which voice index in that trio is the “master” for trigger/pitch; -1 means no unison (each voice independent).

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2. How m_trigs[i] and m_newTrigCanStart[i] are computed

NonagonTrigLogic::SetInput fills the Multi-Phasor Gate input for all 9 voices.

For each voice i:

• Trio and check index – trioId = i / 3. The “logical” voice used for trigger sources is ixToCheck = (m_unisonMaster[trioId] == -1) ? i : m_unisonMaster[trioId] (unison master or self).
• Raw trigger:
  • input.m_trigs[i] = (m_trigOnSubTrigger[trioId] && m_subTrigger[ixToCheck]) || (m_trigOnPitchChanged[trioId] && m_pitchChanged[ixToCheck])
  • So a trigger is requested if the trio is set to trig on sub-trigger and the (master) voice’s index arp triggered, or if the trio is set to trig on pitch-changed and the (master) voice’s LameJuis pitch changed.
• Early-mute – input.m_trigs[i] &= !m_earlyMuted[ixToCheck]. Reserved for future mute logic; currently always false. When true, blocks triggers.
• New-trig-can-start – input.m_newTrigCanStart[i] = m_running && !m_earlyMuted[ixToCheck]. A new note is allowed only when the transport is running and the voice is not early-muted.
• Mute – input.m_mute[i] = m_mute[i] (per-voice mute).
• Interrupt – For each j < i: if m_interrupt[trioId][jTrioId] is true and voice j has a trigger this frame and is not muted (input.m_trigs[j] && !input.m_mute[j]), then set input.m_trigs[i] = false. So a lower-index voice with a trigger can cancel the trigger for voice i when interrupt is enabled between their trios.

Result: m_trigs[i] is true only when the chosen trigger source (pitch-changed or sub-trigger) fired, the note is not early-muted, and no lower-index voice “interrupts” it. m_newTrigCanStart[i] is true when running and not early-muted.

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3. How the Multi-Phasor Gate turns that into m_trig and m_gate

MultiPhasorGateInternal::Process runs once per frame with that input.

Phasor inputs (set by the Nonagon after SetInput):

• m_phasor – Master loop phasor from the Theory of Time.
• m_masterLoopSamples – Master loop length in samples.
• m_phasorDenominator[i] – For each voice, an integer such that the voice’s “period” in master-loop units is 1 / m_phasorDenominator[i] (derived from the voice’s clock and lens so that the gate length matches the voice’s logical step).

Per voice i:

1. Emit trigger – m_ahdControl[i].m_trig = input.m_trigs[i] && input.m_newTrigCanStart[i] && !input.m_mute[i]. So the trigger (what the rest of the synth sees) is true only when: the trigger logic requested a trig, a new trig is allowed, and the voice is not muted. If that is true, m_ahdControl[i].m_release = false.

2. Start gate and bounds – If input.m_trigs[i] && input.m_newTrigCanStart[i]:
   • If not muted: m_gate[i] = true and m_ahdControl[i].m_samples = 0.
   • In all cases: m_preGate[i] = true, m_set[i] = true, and m_bounds[i].Set(input.m_phasor, input.m_phasorDenominator[i]). So we record the current phasor and the voice’s denominator for phase tracking.

3. Envelope timing – envelopeTimeSamples = m_masterLoopSamples / input.m_phasorDenominator[i] (length of one voice “step” in samples). Stored in m_ahdControl[i].m_envelopeTimeSamples.

4. Phase advance and gate off – If m_set[i]:
   • thisPhase = m_bounds[i].Process(input.m_phasor): distance along the circle from the start of this gate to the current phasor, scaled by the voice’s denominator (so 0 -> 1 over one voice period).
   • If thisPhase >= 0.5: gate is turned off (m_gate[i] = false, m_preGate[i] = false). If in addition !input.m_newTrigCanStart[i] || input.m_mute[i], then m_ahdControl[i].m_release = true and m_set[i] = false.
   • m_ahdControl[i].m_samples = thisPhase * envelopeTimeSamples so the AHD envelope sees the correct elapsed time.
5. m_anyGate – If any voice has m_gate[i] true, m_anyGate is true (used e.g. to keep the Theory of Time “running” while a note is held).

So: m_ahdControl[i].m_trig is the single “emit a trigger” flag. The gate m_gate[i] is true from the frame the trigger is accepted until the phasor has advanced half a voice period (0.5 in normalized phase), giving a 50% duty cycle per step unless a new trigger restarts the bounds.

m_gate is not used for envelopes. Envelope attack/hold/decay are driven by m_ahdControl (m_trig, m_samples, m_envelopeTimeSamples, m_release); the DSP copies m_ahdControl into each voice’s AHD input. m_gate is used instead for: (1) note-off and output – when !m_multiPhasorGate.m_gate[i], the Nonagon sets m_output.m_gate[i] = false and records note end; (2) UI – SetGate(i, m_gate[i]) so the interface can show which voices have gate high. So m_gate tracks “note still held” for release timing and display; the envelope sees only AHDControl.

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4. Summary

• Trigger emitted when: trigger logic says trig (pitch-changed or sub-trigger, per trio) and not early-muted and not interrupted by a lower-index voice and m_newTrigCanStart (running, not early-muted) and voice not muted.
• Gate on when a trigger is accepted; gate off when the master phasor has moved 0.5 in the voice’s normalized period (PhasorBounds).
• AHD receives m_trig (start note), m_samples, m_envelopeTimeSamples, and m_release from the same structure, so envelope and voice are driven by this decision.

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Related

• Theory of Time – supplies the master phasor and “any change.”
• LameJuis – supplies pitch and “pitch changed” trigger.
• Glossary – Multi-Phasor Gate, NonagonTrigLogic, AHD, PhasorBounds.
• Documentation index.

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