Amplitude Modulation

Amplitude Modulation involves two oscillators, referred to as the carrier and the modulator, where the modulator controls the carrier's amplitude.

The carrier is typically set at an audible frequency (i.e. 440 Hz) and connected to master output by default. The carrier.amp is set to zero because we will have the modulator control its amplitude.

The modulator is disconnected from master output. Instead, it is connected to the amplitude of the Carrier, like this: carrier.amp(modulator).

In this example...

- MouseX controls the amplitude of the modulator from 0 to 1. When the modulator's amplitude is set to 0, the amplitude modulation has no effect.

- MouseY controls the frequency of the modulator from 0 to 20hz. This range is lower frequencies than humans can hear, and we perceive the modulation as a rhythm. This range can simulate effects such as Tremolo. Ring Modulation is a type of Amplitude Modulation where the original carrier signal is not present, and often involves modulation at a faster frequency.

You will need to include the p5.sound library for this example to work in your own project.

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let carrier; // this is the oscillator we will hear
let modulator; // this oscillator will modulate the amplitude of the carrier
let fft; // we'll visualize the waveform
function setup() {
  createCanvas(800, 400);
  noFill();
  background(30); // alpha
  carrier = new p5.Oscillator(); // connects to master output by default
  carrier.freq(340);
  carrier.amp(0);
  // carrier's amp is 0 by default, giving our modulator total control
  carrier.start();
  modulator = new p5.Oscillator('triangle');
  modulator.disconnect(); // disconnect the modulator from master output
  modulator.freq(5);
  modulator.amp(1);
  modulator.start();
  // Modulate the carrier's amplitude with the modulator
  // Optionally, we can scale the signal.
  carrier.amp(modulator.scale(-1, 1, 1, -1));
  // create an fft to analyze the audio
  fft = new p5.FFT();
}
function draw() {
  background(30, 30, 30, 100); // alpha
  // map mouseY to moodulator freq between 0 and 20hz
  let modFreq = map(mouseY, 0, height, 20, 0);
  modulator.freq(modFreq);
  let modAmp = map(mouseX, 0, width, 0, 1);
  modulator.amp(modAmp, 0.01); // fade time of 0.1 for smooth fading
  // analyze the waveform
  waveform = fft.waveform();
  // draw the shape of the waveform
  drawWaveform();
  drawText(modFreq, modAmp);
}
function drawWaveform() {
  stroke(240);
  strokeWeight(4);
  beginShape();
  for (let i = 0; i < waveform.length; i++) {
    let x = map(i, 0, waveform.length, 0, width);
    let y = map(waveform[i], -1, 1, -height / 2, height / 2);
    vertex(x, y + height / 2);
  }
  endShape();
}
function drawText(modFreq, modAmp) {
  strokeWeight(1);
  text('Modulator Frequency: ' + modFreq.toFixed(3) + ' Hz', 20, 20);
  text('Modulator Amplitude: ' + modAmp.toFixed(3), 20, 40);
}
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Amplitude Modulation