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let sampleRate = 44100.0;
let renderLengthSeconds = 8;
let pulseLengthSeconds = 1;
let pulseLengthFrames = pulseLengthSeconds * sampleRate;
function createSquarePulseBuffer(context, sampleFrameLength) {
let audioBuffer =
context.createBuffer(1, sampleFrameLength, context.sampleRate);
let n = audioBuffer.length;
let data = audioBuffer.getChannelData(0);
for (let i = 0; i < n; ++i)
data[i] = 1;
return audioBuffer;
}
// The triangle buffer holds the expected result of the convolution.
// It linearly ramps up from 0 to its maximum value (at the center)
// then linearly ramps down to 0. The center value corresponds to the
// point where the two square pulses overlap the most.
function createTrianglePulseBuffer(context, sampleFrameLength) {
let audioBuffer =
context.createBuffer(1, sampleFrameLength, context.sampleRate);
let n = audioBuffer.length;
let halfLength = n / 2;
let data = audioBuffer.getChannelData(0);
for (let i = 0; i < halfLength; ++i)
data[i] = i + 1;
for (let i = halfLength; i < n; ++i)
data[i] = n - i - 1;
return audioBuffer;
}
function log10(x) {
return Math.log(x) / Math.LN10;
}
function linearToDecibel(x) {
return 20 * log10(x);
}
// Verify that the rendered result is very close to the reference
// triangular pulse.
function checkTriangularPulse(rendered, reference, should) {
let match = true;
let maxDelta = 0;
let valueAtMaxDelta = 0;
let maxDeltaIndex = 0;
for (let i = 0; i < reference.length; ++i) {
let diff = rendered[i] - reference[i];
let x = Math.abs(diff);
if (x > maxDelta) {
maxDelta = x;
valueAtMaxDelta = reference[i];
maxDeltaIndex = i;
}
}
// allowedDeviationFraction was determined experimentally. It
// is the threshold of the relative error at the maximum
// difference between the true triangular pulse and the
// rendered pulse.
let allowedDeviationDecibels = -124.41;
let maxDeviationDecibels = linearToDecibel(maxDelta / valueAtMaxDelta);
should(
maxDeviationDecibels,
'Deviation (in dB) of triangular portion of convolution')
.beLessThanOrEqualTo(allowedDeviationDecibels);
return match;
}
// Verify that the rendered data is close to zero for the first part
// of the tail.
function checkTail1(data, reference, breakpoint, should) {
let isZero = true;
let tail1Max = 0;
for (let i = reference.length; i < reference.length + breakpoint; ++i) {
let mag = Math.abs(data[i]);
if (mag > tail1Max) {
tail1Max = mag;
}
}
// Let's find the peak of the reference (even though we know a
// priori what it is).
let refMax = 0;
for (let i = 0; i < reference.length; ++i) {
refMax = Math.max(refMax, Math.abs(reference[i]));
}
// This threshold is experimentally determined by examining the
// value of tail1MaxDecibels.
let threshold1 = -129.7;
let tail1MaxDecibels = linearToDecibel(tail1Max / refMax);
should(tail1MaxDecibels, 'Deviation in first part of tail of convolutions')
.beLessThanOrEqualTo(threshold1);
return isZero;
}
// Verify that the second part of the tail of the convolution is
// exactly zero.
function checkTail2(data, reference, breakpoint, should) {
let isZero = true;
let tail2Max = 0;
// For the second part of the tail, the maximum value should be
// exactly zero.
let threshold2 = 0;
for (let i = reference.length + breakpoint; i < data.length; ++i) {
if (Math.abs(data[i]) > 0) {
isZero = false;
break;
}
}
should(isZero, 'Rendered signal after tail of convolution is silent')
.beTrue();
return isZero;
}
function checkConvolvedResult(renderedBuffer, trianglePulse, should) {
let referenceData = trianglePulse.getChannelData(0);
let renderedData = renderedBuffer.getChannelData(0);
let success = true;
// Verify the triangular pulse is actually triangular.
success =
success && checkTriangularPulse(renderedData, referenceData, should);
// Make sure that portion after convolved portion is totally
// silent. But round-off prevents this from being completely
// true. At the end of the triangle, it should be close to
// zero. If we go farther out, it should be even closer and
// eventually zero.
// For the tail of the convolution (where the result would be
// theoretically zero), we partition the tail into two
// parts. The first is the at the beginning of the tail,
// where we tolerate a small but non-zero value. The second part is
// farther along the tail where the result should be zero.
// breakpoint is the point dividing the first two tail parts
// we're looking at. Experimentally determined.
let breakpoint = 12800;
success =
success && checkTail1(renderedData, referenceData, breakpoint, should);
success =
success && checkTail2(renderedData, referenceData, breakpoint, should);
should(success, 'Test signal convolved').message('correctly', 'incorrectly');
}