@sebastbake/music-tempo/src/BeatTracking.ts

Finding out tempo of the music

import Agent from "./Agent";

/**
 * Perform beat tracking on a array of onsets
 * @param {Array} events - the array of onsets to beat track
 * @param {Array} eventsScores - the array of corresponding salience values
 * @param {Array} tempoList - the array of tempo hypothesis
 * @param {Object} [params={}] - parameters
 * @param {Number} [params.initPeriod=5] - duration of the initial section
 * @param {Number} [params.thresholdBI=0.02] - for the purpose of removing duplicate agents, the default JND of IBI
 * @param {Number} [params.thresholdBT=0.04] - for the purpose of removing duplicate agents, the default JND of phase
 * @param {Number} [params.expiryTime=10] - the time after which an Agent that has not accepted any beat will be destroyed
 * @param {Number} [params.toleranceWndInner=0.04] - the maximum time that a beat can deviate from the predicted beat time without a fork occurring
 * @param {Number} [params.toleranceWndPre=0.15] - the maximum amount by which a beat can be earlier than the predicted beat time, expressed as a fraction of the beat period
 * @param {Number} [params.toleranceWndPost=0.3] - the maximum amount by which a beat can be later than the predicted beat time, expressed as a fraction of the beat period
 * @param {Number} [params.correctionFactor=50] - correction factor for updating beat period
 * @param {Number} [params.maxChange=0.2] - the maximum allowed deviation from the initial tempo, expressed as a fraction of the initial beat period
 * @param {Number} [params.penaltyFactor=0.5] - factor for correcting score, if onset do not coincide precisely with predicted beat time
 * @return {Array} agents - agents array
 */

type trackBeatOptions = {
  initPeriod?: number;
  thresholdBI?: number;
  thresholdBT?: number;
  expiryTime?: number;
  toleranceWndInner?: number;
  toleranceWndPre?: number;
  toleranceWndPost?: number;
  correctionFactor?: number;
  maxChange?: number;
  penaltyFactor?: number;
};

const defaultBeatTrackingOptions = {
  initPeriod: 5,
  thresholdBI: 0.02,
  thresholdBT: 0.04,
  expiryTime: 10,
  toleranceWndInner: 0.04,
  toleranceWndPre: 0.15,
  toleranceWndPost: 0.3,
  correctionFactor: 50,
  maxChange: 0.2,
  penaltyFactor: 0.5,
}

export function trackBeat(
  events,
  eventsScores,
  tempoList,
  {
    initPeriod = 5,
    thresholdBI = 0.02,
    thresholdBT = 0.04,
    expiryTime = 10,
    toleranceWndInner = 0.04,
    toleranceWndPre = 0.15,
    toleranceWndPost = 0.3,
    correctionFactor = 50,
    maxChange = 0.2,
    penaltyFactor = 0.5,
  }: trackBeatOptions = defaultBeatTrackingOptions
) {
  let agents: Array<Agent> = [];
  function removeSimilarAgents() {
    agents.sort((a1, a2) => a1.beatInterval - a2.beatInterval);
    const length = agents.length;
    for (let i = 0; i < length; i++) {
      if (agents[i].score < 0) continue;
      for (let j = i + 1; j < length; j++) {
        if (agents[j].beatInterval - agents[i].beatInterval > thresholdBI) {
          break;
        }
        if (Math.abs(agents[j].beatTime - agents[i].beatTime) > thresholdBT) {
          continue;
        }
        if (agents[i].score < agents[j].score) {
          agents[i].score = -1;
        } else {
          agents[j].score = -1;
        }
      }
    }
    for (let i = length - 1; i >= 0; i--) {
      if (agents[i].score < 0) {
        agents.splice(i, 1);
      }
    }
  }

  for (let i = 0; i < tempoList.length; i++) {
    agents.push(
      new Agent(tempoList[i], events[0], eventsScores[0], agents, {
        expiryTime,
        toleranceWndInner,
        toleranceWndPre,
        toleranceWndPost,
        correctionFactor,
        maxChange,
        penaltyFactor,
      })
    );
  }
  let j = 1;
  removeSimilarAgents();

  while (events[j] < initPeriod) {
    let agentsLength = agents.length;
    let prevBeatInterval = -1;
    let isEventAccepted = true;
    for (let k = 0; k < agentsLength; k++) {
      if (agents[k].beatInterval != prevBeatInterval) {
        if (!isEventAccepted) {
          agents.push(
            new Agent(prevBeatInterval, events[j], eventsScores[j], agents, {
              expiryTime,
              toleranceWndInner,
              toleranceWndPre,
              toleranceWndPost,
              correctionFactor,
              maxChange,
              penaltyFactor,
            })
          );
        }
        prevBeatInterval = agents[k].beatInterval;
        isEventAccepted = false;
      }
      isEventAccepted =
        agents[k].considerEvent(events[j], eventsScores[j]) || isEventAccepted;
    }
    removeSimilarAgents();
    j++;
  }
  const eventsLength = events.length;
  for (let i = j; i < eventsLength; i++) {
    let agentsLength = agents.length;
    for (let j = 0; j < agentsLength; j++) {
      agents[j].considerEvent(events[i], eventsScores[i]);
    }
    removeSimilarAgents();
  }

  return agents;
}