Pulse

import {
  chord,
  defineCue,
  gain,
  lowPass,
  mix,
  normalize,
  note,
  pad,
  sequence,
  shape,
  sine,
  step,
  type CueDefinition,
} from "odori";

export type BedPulseOptions = {
  /** Tempo of the pulse. Slower reads calmer under narration. */
  bpm?: number;
  /** Root of the held chord, as a note name. */
  root?: string;
  /** Peak level before the mix normalizes the whole track. */
  peak?: number;
};

/**
 * Two bars of soft repeating pulse: a held minor seventh underneath, and a
 * muted low tone on each beat to give the bed a heartbeat without giving it a
 * groove. Written to sit under a voice, so nothing in it competes for the
 * frequencies a voice uses.
 *
 * It loops, so the placement repeats it for as long as the scene runs and the
 * score is rendered once.
 */
export const bedPulse = ({bpm = 84, root = "c2", peak = 0.55}: BedPulseOptions = {}): CueDefinition => {
  const beat = step(bpm, 4);
  const bars = 2;
  const samples = beat * 4 * bars;

  return defineCue({
    name: "bed.pulse",
    // Two bars at this tempo, in frames at 30fps.
    durationInFrames: Math.round((samples / 48000) * 30),
    loops: true,
    params: {bpm, root, peak},
    render: () =>
      normalize(
        mix(
          // The held chord, low passed so it stays under everything else.
          gain(lowPass(pad(chord(root, "minor7"), samples, {envelope: {attack: 0.9, sustain: 1, release: 0.9}}), 900), 0.9),
          // The pulse itself: one soft tone per beat, decaying immediately.
          sequence(
            Array.from({length: 4 * bars}, (_, index) => ({
              at: index,
              play: (length: number) =>
                shape(sine(length, note(root) * 2), {attack: 0.01, decay: 0.35, sustain: 0, release: 0.1}),
              // The downbeat is louder, which is what makes four beats read as a bar.
              gain: index % 4 === 0 ? 0.5 : 0.28,
            })),
            {bpm, samples},
          ),
        ),
        peak,
      ),
  });
};

import {CueWave, defineComponentPreview} from "odori/preview";
import {bedPulse, type BedPulseOptions} from "./bed-pulse";

const Wave = ({bpm, root, peak}: BedPulseOptions) => <CueWave cue={bedPulse({bpm, root, peak})} />;

export default defineComponentPreview({
  title: "Pulse",
  category: "Sound/Beds",
  description: "A repeating pulse over a sustained chord.",
  component: Wave,
  canvas: {width: 1920, height: 1080, duration: "5s"},
  controls: {
    bpm: {type: "number", defaultValue: 84, min: 64, max: 112, step: 4},
    root: {type: "select", defaultValue: "c2", options: ["a1", "c2", "d2", "f2"]},
    peak: {type: "number", defaultValue: 0.55, min: 0.1, max: 1, step: 0.05},
  },
  examples: [{name: "Default", props: {}}, {name: "Slower", props: {bpm: 72}}],
});

import {Scene, Video} from "odori";
import {BedPulse} from "../components/bed-pulse/bed-pulse";

<Video>
  <Scene id="bed-pulse" duration="5.7s">
    <BedPulse />
  </Scene>
</Video>