Semi-accurate TR808 rimshot

rimshot.js

/*
    Semi-accurate TR808 rimshot

    ISC License

    Copyright 2025 Polyzium

    Permission to use, copy, modify, and/or distribute this software for any purpose
    with or without fee is hereby granted, provided that the above copyright notice
    and this permission notice appear in all copies.

    THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
    REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
    FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT,
    OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
    DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
    ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/

class RS {
    constructor() {
        this.phase1 = 0;
        this.phase2 = 0;
        this.env1 = 0;
        this.env2 = 0;
        this.aOut = 0;
        this.aOutPrev = 0;
        this.aInPrev = 0;
    }

    trigger() {
        this.env1 = 1;
        this.env2 = 1;
        this.phase1 = 0;
        this.phase2 = 0;
    }

    process(sampleRate) {
        this.outPrev = this.out;

        this.phase1 += 455 / sampleRate;
        this.phase2 += 1667 / sampleRate;
        if (this.phase1 > 1) this.phase1 -= 1;
        if (this.phase2 > 1) this.phase2 -= 1;

        this.env1 *= Math.exp(-1000 / (3 * sampleRate));
        this.env2 *= Math.exp(-1000 / (2 * sampleRate));

        const osc1 = Math.sin(this.phase1 * 2 * Math.PI) * this.env1;
        const osc2 = Math.sin(this.phase2 * 2 * Math.PI) * this.env2;

        let oscmix = (osc1 + osc2);
        
        const drive = 12;
        const bias = -0.43;
        
        // Simple hard clip distortion
        let aIn = oscmix * drive + bias;
        aIn = Math.min(Math.max(aIn, -1), 1);
        
        // DC blocker
        const R = 0.997;
        this.aOut = aIn - this.aInPrev + R * this.aOutPrev;
        this.aInPrev = aIn;
        this.aOutPrev = this.aOut;

        return this.aOut;
    }
}

const rs = new RS();

return function (time, sampleRate) {
	const t = Math.round(time * sampleRate);
    const currentSecond = Math.floor(time);
    if (t % sampleRate == 0) {
        rs.trigger();
        lastTime = currentSecond;
    }

    return rs.process(sampleRate);
}