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December 14, 2021 17:47
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An example Elementary pattern for writing "MIDI Events" to an in-memory sequence-based synthesizer that ultimately renders its output as a series of el.seq nodes.
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| // A simple polyphonic Synth which records note events against internal | |
| // sequence data. | |
| // | |
| // After recording a series of events, call the render function to build | |
| // a series of synth voices based on the aggregated sequence data. | |
| export default class Synth { | |
| constructor(key, numVoices) { | |
| this.voices = Array.from({length: numVoices}).map(function(x, i) { | |
| return { | |
| key: `${key}:v:${i}`, | |
| gate: 0, | |
| freq: 440, | |
| velo: 0, | |
| data: { | |
| gateSeq: [], | |
| freqSeq: [], | |
| veloSeq: [], | |
| } | |
| }; | |
| }); | |
| this.nextVoice = 0; | |
| } | |
| step() { | |
| this.voices.forEach(function(voice, i) { | |
| voice.data.gateSeq.push(voice.gate); | |
| voice.data.freqSeq.push(voice.freq); | |
| voice.data.veloSeq.push(voice.velo); | |
| }) | |
| } | |
| noteOn(freq, velo) { | |
| this.voices[this.nextVoice].gate = 1.0; | |
| this.voices[this.nextVoice].freq = freq; | |
| this.voices[this.nextVoice].velo = velo; | |
| if (++this.nextVoice >= this.voices.length) { | |
| this.nextVoice -= this.voices.length; | |
| } | |
| } | |
| noteOff(freq) { | |
| for (let i = 0; i < this.voices.length; ++i) { | |
| if (this.voices[i].freq === freq) { | |
| this.voices[i].gate = 0; | |
| } | |
| } | |
| } | |
| render(renderFunc) { | |
| return this.voices.map(function(voice, i) { | |
| return renderFunc(voice.key, voice.data.gateSeq, voice.data.freqSeq, voice.data.veloSeq, i); | |
| }); | |
| } | |
| } |
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| let syn = new Synth('syn', 4); | |
| let lastTick = 0; | |
| // Imagine we have a big array of midi events here and want to iterate | |
| // over it, acting against our synth instance | |
| for (let i = 0; i < events.length; ++i) { | |
| // We want our synth to understand how many midi ticks have passed since the last event, | |
| // so we "step" as many times as necessary to arrive at the current event time | |
| while (lastTick < events[i].tickTime) { | |
| syn.step(); | |
| } | |
| // Now we can record our current event | |
| if (events[i].type === 'noteOn') { | |
| syn.noteOn(events[i].noteFrequency, events[i].velocity); | |
| } | |
| if (events[i].type === 'noteOff') { | |
| syn.noteOff(events[i].noteFrequench); | |
| } | |
| } | |
| // Finally we can render our poly-voice pattern with whatever we want: | |
| core.render( | |
| el.add(...syn.render(function(key, gs, fs, vs, i) { | |
| let t = el.metro({interval: 20}); | |
| let env = el.adsr(0.01, 0.1, 0, 0.1, el.seq({key: `${key}:gs`, seq: gs, hold: true}, t)); | |
| let tone = el.cycle(el.seq({key: `${key}:fs`, seq: fs, hold: true}, t)); | |
| return el.mul(env, tone); | |
| }); | |
| ); |
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