{ "$type": "at.atmosynth.module", "descriptionVersion": 1, "moduleId": "filter-comb", "versionKey": "2", "name": "Comb filter", "description": "A filter tuned to a pitch rather than set to a cutoff. It delays the sound by exactly one period of that pitch and adds it back to itself, so everything at the pitch and its harmonics reinforces and everything between cancels — a whole row of peaks and notches at once, which is the sound of a short room, a cardboard tube, or a plucked string depending on how much of it goes round again. Resonance is how much: near one it rings on into a pitch of its own long after the sound that started it, and below nothing the feedback is subtracted instead, which shifts every notch by half a spacing and leaves the hollow, woody sound an octave below where you would expect it. Damping takes a little more of the top off each time round, so the ring dies from the treble down as a string does rather than all at once. Pitch is an input as well as a knob and Pitch depth is how far, in cents — an LFO patched in is a flanger you wired yourself — and Key tracking moves the tuning with the note played, which needs the note routed here: at one the comb rings in tune with whatever is played through it. This module carries code, for the one thing the node vocabulary cannot do: a comb's delay is one divided by its pitch, and nothing in that vocabulary divides. Resonance is an input as well, and its depth how far a signal there moves it; the comb holds what arrives inside the knob's own range, so the ring never runs away.", "audioInputs": [ { "id": "in", "label": "In" }, { "id": "pitch", "label": "Pitch" }, { "id": "resonance", "label": "Resonance" } ], "audioOutputs": [ { "id": "out", "label": "Out" } ], "midiInputs": [ { "id": "midi", "label": "Note" } ], "nodes": [ { "id": "in", "kind": "moduleInput", "options": { "input": "in" } }, { "id": "gen", "kind": "audioWorklet", "options": { "code": "// A comb filter: one delay line fed back into itself, tuned in hertz.\n//\n// The delay and the feedback are both ordinary nodes, and the sound is\n// reachable without code — the Delay module is that patch. What is not\n// reachable is the knob. A comb's delay is the *reciprocal* of the pitch it\n// rings at, and the node vocabulary sums and scales signals; it does not\n// divide one. So nothing built from it can put a frequency on the knob, sweep\n// the tuning evenly in cents, or take its pitch from the note played — and a\n// comb that cannot be tuned is a very short delay, which the library already\n// has. The reciprocal is the whole reason this one carries code.\n//\n// One period of delay, read back with the two samples either side of the\n// fractional position mixed in proportion: at 3 kHz a period is sixteen\n// samples, and rounding to the nearer of them would put the ringing a\n// semitone out and step audibly as it swept.\n//\n// The feedback runs through a single pole of lowpass, so each pass round the\n// loop loses a little more of the top than the last. That is what a plucked\n// string does and what a bare comb does not: undamped, the highest partials\n// ring exactly as long as the lowest, which sounds like a metal tube rather\n// than anything with a body.\nconst clamp = (value, low, high) => (value < low ? low : value > high ? high : value);\n\nclass AtmosynthComb extends AudioWorkletProcessor {\n static get parameterDescriptors() {\n return [\n { name: 'frequency', defaultValue: 220, minValue: 20, maxValue: 8000, automationRate: 'a-rate' },\n { name: 'detune', defaultValue: 0, minValue: -4800, maxValue: 4800, automationRate: 'a-rate' },\n // Negative is the other polarity, not less of the same one: the feedback\n // subtracted rather than added moves every notch half a spacing and\n // leaves the odd harmonics, which is the hollow, half-pitched sound.\n { name: 'resonance', defaultValue: 0.6, minValue: -0.95, maxValue: 0.95, automationRate: 'a-rate' },\n { name: 'damping', defaultValue: 0.2, minValue: 0, maxValue: 1, automationRate: 'a-rate' },\n ];\n }\n\n constructor() {\n super();\n // A twentieth of a second of line, which is one period of the lowest\n // tuning the knob reaches, at whatever rate this context runs at.\n this.line = new Float32Array(Math.ceil(sampleRate / 20) + 4);\n this.write = 0;\n this.damped = 0;\n }\n\n process(inputs, outputs, parameters) {\n const output = outputs[0];\n const channel = output[0];\n const source = inputs[0] && inputs[0][0] ? inputs[0][0] : null;\n const at = (values, index) => (values.length > 1 ? values[index] : values[0]);\n const line = this.line;\n const size = line.length;\n\n for (let index = 0; index < channel.length; index += 1) {\n const hz = clamp(\n at(parameters.frequency, index) * Math.pow(2, at(parameters.detune, index) / 1200),\n 20,\n sampleRate / 4,\n );\n // The reciprocal: one period of that pitch, in samples.\n const period = clamp(sampleRate / hz, 2, size - 2);\n let read = this.write - period;\n if (read < 0) read += size;\n const whole = Math.floor(read);\n const next = whole + 1 >= size ? 0 : whole + 1;\n const fraction = read - whole;\n const delayed = line[whole] + (line[next] - line[whole]) * fraction;\n\n // At nothing the pole passes everything and the comb rings evenly; at\n // one it keeps a fiftieth of each pass, and the ring is over almost\n // before it starts.\n const opening = 1 - at(parameters.damping, index) * 0.98;\n this.damped += opening * (delayed - this.damped);\n\n const value =\n (source ? source[index] : 0) + at(parameters.resonance, index) * this.damped;\n line[this.write] = value;\n this.write = this.write + 1 >= size ? 0 : this.write + 1;\n channel[index] = value;\n }\n\n for (let other = 1; other < output.length; other += 1) output[other].set(channel);\n return true;\n }\n}\n\nregisterProcessor('atmosynth-comb', AtmosynthComb);\n", "declaredParams": [ { "default": 220, "max": 8000, "min": 20, "name": "frequency" }, { "default": 0, "max": 4800, "min": -4800, "name": "detune" }, { "default": "0.6", "max": "0.95", "min": "-0.95", "name": "resonance" }, { "default": "0.2", "max": 1, "min": 0, "name": "damping" } ], "numberOfInputs": 1, "numberOfOutputs": 1, "processorName": "atmosynth-comb" } }, { "id": "pitchin", "kind": "moduleInput", "options": { "input": "pitch" } }, { "id": "pitchdepth", "kind": "gain", "options": {} }, { "id": "note", "kind": "midiInput", "options": { "midiInput": "midi" } }, { "id": "trackdepth", "kind": "gain", "options": {} }, { "id": "trim", "kind": "gain", "options": {} }, { "id": "out", "kind": "moduleOutput", "options": { "output": "out" } }, { "id": "resonancein", "kind": "moduleInput", "options": { "input": "resonance" } }, { "id": "resonancedepth", "kind": "gain", "options": {} } ], "connections": [ { "from": { "node": "in", "output": 0 }, "to": { "node": "gen", "input": 0 } }, { "from": { "node": "gen", "output": 0 }, "to": { "node": "trim", "input": 0 } }, { "from": { "node": "trim", "output": 0 }, "to": { "node": "out", "input": 0 } }, { "from": { "node": "pitchin", "output": 0 }, "to": { "node": "pitchdepth", "input": 0 } }, { "from": { "node": "pitchdepth", "output": 0 }, "to": { "node": "gen", "param": "detune" } }, { "from": { "node": "note", "output": 0 }, "to": { "node": "trackdepth", "input": 0 } }, { "from": { "node": "trackdepth", "output": 0 }, "to": { "node": "gen", "param": "frequency" } }, { "from": { "node": "resonancein", "output": 0 }, "to": { "node": "resonancedepth", "input": 0 } }, { "from": { "node": "resonancedepth", "output": 0 }, "to": { "node": "gen", "param": "resonance" } } ], "automation": [], "parameters": [ { "id": "pitch", "label": "Pitch (Hz)", "range": { "min": "20", "max": "8000" }, "default": "220", "targets": [ { "node": "gen", "param": "frequency" } ] }, { "id": "resonance", "label": "Resonance (below nothing to invert)", "range": { "min": "-0.95", "max": "0.95" }, "default": "0.6", "targets": [ { "node": "gen", "param": "resonance" } ] }, { "id": "damping", "label": "Damping", "range": { "min": "0", "max": "1" }, "default": "0.2", "targets": [ { "node": "gen", "param": "damping" } ] }, { "id": "pitchAmount", "label": "Pitch depth (cents)", "range": { "min": "-4800", "max": "4800" }, "default": "1200", "targets": [ { "node": "pitchdepth", "param": "gain" } ] }, { "id": "keyTrack", "label": "Key tracking", "range": { "min": "0", "max": "2" }, "default": "0", "targets": [ { "node": "trackdepth", "param": "gain" } ] }, { "id": "level", "label": "Level", "range": { "min": "0", "max": "2" }, "default": "0.5", "targets": [ { "node": "trim", "param": "gain" } ] }, { "id": "resonanceAmount", "label": "Resonance depth", "range": { "min": "-1.9", "max": "1.9" }, "default": "0.4", "targets": [ { "node": "resonancedepth", "param": "gain" } ] } ], "sampleSlots": [], "createdAt": "2026-09-21T00:00:00.000Z" }