From c3cd5d08c9d2e315890b4b215fdce9039ceb7379 Mon Sep 17 00:00:00 2001
From: Raphael Forment <raphael.forment@gmail.com>
Date: Tue, 29 Aug 2023 17:25:27 +0200
Subject: [PATCH] adding linear and exponential envelope for fm synthesis

---
 packages/superdough/helpers.mjs | 13 ++++++++++
 packages/superdough/synth.mjs   | 45 +++++++++++++++++++++++----------
 2 files changed, 44 insertions(+), 14 deletions(-)

diff --git a/packages/superdough/helpers.mjs b/packages/superdough/helpers.mjs
index 7cc54c8d..e07f0d7d 100644
--- a/packages/superdough/helpers.mjs
+++ b/packages/superdough/helpers.mjs
@@ -39,6 +39,19 @@ export const getEnvelope = (attack, decay, sustain, release, velocity, begin) =>
   };
 };
 
+export const getExpEnvelope = (attack, decay, velocity, begin) => {
+  const gainNode = getAudioContext().createGain();
+  gainNode.gain.setValueAtTime(0.0001, begin);
+  gainNode.gain.exponentialRampToValueAtTime(velocity, begin + attack);
+  gainNode.gain.exponentialRampToValueAtTime(0.0001, begin + attack + decay);
+  return {
+    node: gainNode,
+    stop: (t) => {
+      gainNode.gain.exponentialRampToValueAtTime(0.0001, t + decay);
+    },
+  };
+};
+
 export const getADSR = (attack, decay, sustain, release, velocity, begin, end) => {
   const gainNode = getAudioContext().createGain();
   gainNode.gain.setValueAtTime(0, begin);
diff --git a/packages/superdough/synth.mjs b/packages/superdough/synth.mjs
index 4ef9ddb8..d8f9890f 100644
--- a/packages/superdough/synth.mjs
+++ b/packages/superdough/synth.mjs
@@ -1,8 +1,22 @@
 import { midiToFreq, noteToMidi } from './util.mjs';
 import { registerSound, getAudioContext } from './superdough.mjs';
-import { getOscillator, gainNode, getEnvelope } from './helpers.mjs';
+import { getOscillator, gainNode, getEnvelope, getExpEnvelope } from './helpers.mjs';
+
+const fm = (osc, harmonicityRatio, modulationIndex, wave) => {
+	/*
+	 * This function helps to setup a modulator for FM Synthesis
+	 * @returns a modulator
+	 */
+  const carrfreq = osc.frequency.value;
+  const modfreq = carrfreq * harmonicityRatio;
+  const modgain = modfreq * modulationIndex;
+  return mod(modfreq, modgain, wave);
+};
 
 const mod = (freq, range = 1, type) => {
+	/*
+	 * This function creates an oscillator
+	 */
   const ctx = getAudioContext();
   const osc = ctx.createOscillator();
   osc.type = type;
@@ -13,12 +27,6 @@ const mod = (freq, range = 1, type) => {
   return { node: g, stop: (t) => osc.stop(t) };
 };
 
-const fm = (osc, harmonicityRatio, modulationIndex, wave) => {
-  const carrfreq = osc.frequency.value;
-  const modfreq = carrfreq * harmonicityRatio;
-  const modgain = modfreq * modulationIndex;
-  return mod(modfreq, modgain, wave);
-};
 
 export function registerSynthSounds() {
   ['sine', 'square', 'triangle', 'sawtooth'].forEach((wave) => {
@@ -33,6 +41,12 @@ export function registerSynthSounds() {
           release = 0.01,
           fmh: fmHarmonicity = 1,
           fmi: fmModulationIndex,
+					fmenv: fmEnvelopeType = 'linear',
+					fmattack: fmAttack = 0.001,
+					fmdecay: fmDecay = 0.2,
+					fmsustain: fmSustain = 0.001,
+					fmrelease: fmRelease = 0.1,
+					fmvelocity: fmVelocity = 1,
 					fmwave: fmWaveform = 'sine'
         } = value;
         let { n, note, freq } = value;
@@ -49,14 +63,17 @@ export function registerSynthSounds() {
         // make oscillator
         const { node: o, stop } = getOscillator({ t, s: wave, freq });
 
-        let stopFm;
+        let stopFm, fmEnvelope;
         if (fmModulationIndex) {
-          const { node: modulator, stop } = fm(
-						o, fmHarmonicity, 
-						fmModulationIndex, 
-						fmWaveform
-					);
-          modulator.connect(o.frequency);
+          const { node: modulator, stop } = fm( o, fmHarmonicity, fmModulationIndex, fmWaveform);
+					fmEnvelope = getEnvelope(fmAttack, fmDecay, fmSustain, fmRelease, fmVelocity, t);
+					if (fmEnvelopeType === "exp") {
+						fmEnvelope = getExpEnvelope(fmAttack, fmDecay, fmVelocity, t);
+						fmEnvelope.node.maxValue = fmModulationIndex * 2;
+						fmEnvelope.node.minValue = 0.00001;
+					}
+					modulator.connect(fmEnvelope.node);
+          fmEnvelope.node.connect(o.frequency);
           stopFm = stop;
         }
         const g = gainNode(0.3);