src/BeatTracking.js | API Document

# src/BeatTracking.js

    import Agent from "./Agent";
    /**
     * Performs automatic beat tracking
     * @class
     */
    export default class BeatTracking {
        /**
         * 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
         */
        static trackBeat(events, eventsScores, tempoList, params = {}) {
            const   initPeriod = params.initPeriod || 5,
                    thresholdBI = params.thresholdBI || 0.02,
                    thresholdBT = params.thresholdBT || 0.04;
            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);
                    }
                }
            }
            var agents = [];

            for (let i = 0; i < tempoList.length; i++) {
                agents.push(new Agent(tempoList[i], events[0], eventsScores[0], agents, params));
            }
            var 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, params));
                        }
                        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;
        }
    }