HoastBinauralDecoder.js

// this file is based on ambi-binauralDecoder.js from JSAmbisonics
// adapted to be used with HOAST360
//
// Use HOASTBinDecoder to do binaural decoding via convolution
// of an SH domain signal with SH decoding filters.
// This uses a separate buffer for first-order filters, so they are 
// allowed to differ in length w.r.t. higher-order filters.
//
// Thomas Deppisch, 2020

////////////////////////////////////////////////////////////////////
//  Archontis Politis
//  archontis.politis@aalto.fi
//  David Poirier-Quinot
//  davipoir@ircam.fr
////////////////////////////////////////////////////////////////////
//
//  JSAmbisonics a JavaScript library for higher-order Ambisonics
//  The library implements Web Audio blocks that perform
//  typical ambisonic processing operations on audio signals.
//
////////////////////////////////////////////////////////////////////

export default class HOASTBinDecoder {

    constructor(audioCtx, order) {

        this.initialized = false;

        this.ctx = audioCtx;
        this.order = order;
        this.nCh = (order + 1) * (order + 1);
        this.decFilters = new Array(this.nCh);
        this.decFilterNodes = new Array(this.nCh);
        // input and output nodes
        this.in = this.ctx.createChannelSplitter(this.nCh);
        this.out = this.ctx.createChannelMerger(2);
        this.out.channelCountMode = 'explicit';
        this.out.channelCount = 1;
        // downmixing gains for left and right ears
        this.gainMid = this.ctx.createGain();
        this.gainSide = this.ctx.createGain();
        this.invertSide = this.ctx.createGain();
        this.gainMid.gain.value = 1;
        this.gainSide.gain.value = 1;
        this.invertSide.gain.value = -1;
        // convolver nodes
        for (let i = 0; i < this.nCh; i++) {
            this.decFilterNodes[i] = this.ctx.createConvolver();
            this.decFilterNodes[i].normalize = false;
        }
        // initialize convolvers to plain cardioids
        this.resetFilters();
        // create audio connections
        for (let i = 0; i < this.nCh; i++) {
            this.in.connect(this.decFilterNodes[i], i, 0);
            var n = Math.floor(Math.sqrt(i));
            var m = i - n * n - n;
            if (m >= 0) this.decFilterNodes[i].connect(this.gainMid);
            else this.decFilterNodes[i].connect(this.gainSide);
        }
        this.gainMid.connect(this.out, 0, 0);
        this.gainSide.connect(this.out, 0, 0);

        this.gainMid.connect(this.out, 0, 1);
        this.gainSide.connect(this.invertSide, 0, 0);
        this.invertSide.connect(this.out, 0, 1);

        this.initialized = true;
    }

    updateFilters(foaBuffer, hoaBuffer) {
        // assign filters to convolvers
        // foaBuffer
        for (let i = 0; i < 4; ++i) {
            this.decFilters[i] = this.ctx.createBuffer(1, foaBuffer.length, foaBuffer.sampleRate);
            this.decFilters[i].getChannelData(0).set(foaBuffer.getChannelData(i));
            this.decFilterNodes[i].buffer = this.decFilters[i];
        }
        // hoaBuffer
        for (let i = 4; i < this.nCh; ++i) {
            this.decFilters[i] = this.ctx.createBuffer(1, hoaBuffer.length, hoaBuffer.sampleRate);
            this.decFilters[i].getChannelData(0).set(hoaBuffer.getChannelData(i - 4));
            this.decFilterNodes[i].buffer = this.decFilters[i];
        }
    }

    resetFilters() {
        // overwrite decoding filters (plain cardioid virtual microphones)
        var cardGains = new Array(this.nCh);
        cardGains.fill(0);
        cardGains[0] = 0.5;
        cardGains[1] = 0.5 / Math.sqrt(3);
        for (var i = 0; i < this.nCh; i++) {
            // ------------------------------------
            // This works for Chrome and Firefox:
            // this.decFilters[i] = this.ctx.createBuffer(1, 1, this.ctx.sampleRate);
            // this.decFilters[i].getChannelData(0).set([cardGains[i]]);
            // ------------------------------------
            // Safari forces us to use this:
            this.decFilters[i] = this.ctx.createBuffer(1, 64, this.ctx.sampleRate);
            // and will send gorgeous crancky noise bursts for any value below 64
            for (var j = 0; j < 64; j++) {
                this.decFilters[i].getChannelData(0)[j] = 0.0;
            }
            this.decFilters[i].getChannelData(0)[0] = cardGains[i];
            // ------------------------------------
            this.decFilterNodes[i].buffer = this.decFilters[i];
        }
    }
}