44 lines
1.6 KiB
JavaScript
44 lines
1.6 KiB
JavaScript
// Define functions that implement the formulas for AudioParam automations.
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// AudioParam linearRamp value at time t for a linear ramp between (t0, v0) and
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// (t1, v1). It is assumed that t0 <= t. Results are undefined otherwise.
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function audioParamLinearRamp(t, v0, t0, v1, t1) {
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if (t >= t1)
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return v1;
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return (v0 + (v1 - v0) * (t - t0) / (t1 - t0))
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}
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// AudioParam exponentialRamp value at time t for an exponential ramp between
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// (t0, v0) and (t1, v1). It is assumed that t0 <= t. Results are undefined
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// otherwise.
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function audioParamExponentialRamp(t, v0, t0, v1, t1) {
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if (t >= t1)
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return v1;
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return v0 * Math.pow(v1 / v0, (t - t0) / (t1 - t0));
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}
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// AudioParam setTarget value at time t for a setTarget curve starting at (t0,
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// v0) with a final value of vFainal and a time constant of timeConstant. It is
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// assumed that t0 <= t. Results are undefined otherwise.
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function audioParamSetTarget(t, v0, t0, vFinal, timeConstant) {
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return vFinal + (v0 - vFinal) * Math.exp(-(t - t0) / timeConstant);
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}
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// AudioParam setValueCurve value at time t for a setValueCurve starting at time
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// t0 with curve, curve, and duration duration. The sample rate is sampleRate.
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// It is assumed that t0 <= t.
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function audioParamSetValueCurve(t, curve, t0, duration) {
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if (t > t0 + duration)
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return curve[curve.length - 1];
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let curvePointsPerSecond = (curve.length - 1) / duration;
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let virtualIndex = (t - t0) * curvePointsPerSecond;
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let index = Math.floor(virtualIndex);
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let delta = virtualIndex - index;
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let c0 = curve[index];
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let c1 = curve[Math.min(index + 1, curve.length - 1)];
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return c0 + (c1 - c0) * delta;
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}
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