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fix(analysis): detect effective spectral cutoff

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zarzet
2026-07-28 21:15:06 +07:00
parent 1bf61884cd
commit b1c18b95e7
3 changed files with 323 additions and 94 deletions
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test/audio_analysis_spectrogram_test.dart
+98 -29
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@@ -117,17 +117,40 @@ lavfi.r128.true_peak=0.907
expect(arguments, isNot(contains('-ac')));
expect(arguments, isNot(contains('-loglevel')));
});
test('renders a monotonic cutoff plane beside the display image', () {
final arguments = buildAudioSpectrogramArguments(
inputPath: 'source.flac',
outputPath: 'spectrum.rgba',
cutoffOutputPath: 'cutoff.gray',
);
final filter = arguments[arguments.indexOf('-filter_complex') + 1];
expect(filter, contains('asplit=2'));
expect(filter, contains('color=intensity'));
expect(filter, contains('s=400x800'));
expect(filter, contains('color=green'));
expect(filter, contains('format=gray[cutoff]'));
expect(
arguments,
containsAllInOrder(['-map', '[cutoff]', '-frames:v', '1']),
);
expect(
arguments,
containsAllInOrder(['-pix_fmt', 'gray', 'cutoff.gray']),
);
});
});
group('broadband spectral cutoff', () {
group('effective spectral cutoff', () {
const width = 200;
const height = 800;
const nyquist = 96000.0;
test('ignores a narrow ultrasonic pilot above a 22 kHz music band', () {
final rgba = _blankRgba(width, height);
final intensity = _blankIntensity(width, height, value: 12);
_paintFrequencyBand(
rgba,
intensity,
width: width,
height: height,
maxFrequencyHz: nyquist,
@@ -136,7 +159,7 @@ lavfi.r128.true_peak=0.907
intensity: 220,
);
_paintFrequencyBand(
rgba,
intensity,
width: width,
height: height,
maxFrequencyHz: nyquist,
@@ -145,8 +168,8 @@ lavfi.r128.true_peak=0.907
intensity: 255,
);
final cutoff = estimateBroadbandSpectralCutoffHz(
rgba: rgba,
final cutoff = estimateEffectiveSpectralCutoffHz(
intensity: intensity,
width: width,
height: height,
maxFrequencyHz: nyquist,
@@ -156,10 +179,45 @@ lavfi.r128.true_peak=0.907
expect(cutoff!, inInclusiveRange(21000, 23500));
});
test('retains genuine broadband ultrasonic content', () {
final rgba = _blankRgba(width, height);
test('rejects a low noise floor above a 15.8 kHz bandwidth edge', () {
const cdNyquist = 22050.0;
final intensity = _blankIntensity(width, height, value: 42);
_paintFrequencyBand(
rgba,
intensity,
width: width,
height: height,
maxFrequencyHz: cdNyquist,
lowHz: 0,
highHz: 15800,
intensity: 100,
);
_paintFrequencyBand(
intensity,
width: width,
height: height,
maxFrequencyHz: cdNyquist,
lowHz: 15800,
highHz: cdNyquist,
intensity: 85,
startColumn: 0,
endColumn: 10,
);
final cutoff = estimateEffectiveSpectralCutoffHz(
intensity: intensity,
width: width,
height: height,
maxFrequencyHz: cdNyquist,
);
expect(cutoff, isNotNull);
expect(cutoff!, inInclusiveRange(15300, 16300));
});
test('retains genuine broadband ultrasonic content', () {
final intensity = _blankIntensity(width, height, value: 10);
_paintFrequencyBand(
intensity,
width: width,
height: height,
maxFrequencyHz: nyquist,
@@ -168,8 +226,8 @@ lavfi.r128.true_peak=0.907
intensity: 180,
);
final cutoff = estimateBroadbandSpectralCutoffHz(
rgba: rgba,
final cutoff = estimateEffectiveSpectralCutoffHz(
intensity: intensity,
width: width,
height: height,
maxFrequencyHz: nyquist,
@@ -179,10 +237,23 @@ lavfi.r128.true_peak=0.907
expect(cutoff!, inInclusiveRange(47000, 49500));
});
test('reports Nyquist for full-bandwidth content', () {
final intensity = _blankIntensity(width, height, value: 180);
final cutoff = estimateEffectiveSpectralCutoffHz(
intensity: intensity,
width: width,
height: height,
maxFrequencyHz: nyquist,
);
expect(cutoff, nyquist);
});
test('does not report an isolated line as a broadband cutoff', () {
final rgba = _blankRgba(width, height);
final intensity = _blankIntensity(width, height);
_paintFrequencyBand(
rgba,
intensity,
width: width,
height: height,
maxFrequencyHz: nyquist,
@@ -191,8 +262,8 @@ lavfi.r128.true_peak=0.907
intensity: 255,
);
final cutoff = estimateBroadbandSpectralCutoffHz(
rgba: rgba,
final cutoff = estimateEffectiveSpectralCutoffHz(
intensity: intensity,
width: width,
height: height,
maxFrequencyHz: nyquist,
@@ -203,8 +274,8 @@ lavfi.r128.true_peak=0.907
test('rejects invalid or incomplete images', () {
expect(
estimateBroadbandSpectralCutoffHz(
rgba: Uint8List(3),
estimateEffectiveSpectralCutoffHz(
intensity: Uint8List(0),
width: 1,
height: 1,
maxFrequencyHz: nyquist,
@@ -215,31 +286,29 @@ lavfi.r128.true_peak=0.907
});
}
Uint8List _blankRgba(int width, int height) {
final rgba = Uint8List(width * height * 4);
for (var offset = 3; offset < rgba.length; offset += 4) {
rgba[offset] = 255;
}
return rgba;
Uint8List _blankIntensity(int width, int height, {int value = 0}) {
final intensity = Uint8List(width * height);
if (value > 0) intensity.fillRange(0, intensity.length, value);
return intensity;
}
void _paintFrequencyBand(
Uint8List rgba, {
Uint8List values, {
required int width,
required int height,
required double maxFrequencyHz,
required double lowHz,
required double highHz,
required int intensity,
int startColumn = 0,
int? endColumn,
}) {
final columnEnd = endColumn ?? width;
for (var y = 0; y < height; y++) {
final frequency = (height - y - 0.5) / height * maxFrequencyHz;
if (frequency < lowHz || frequency > highHz) continue;
for (var x = 0; x < width; x++) {
final offset = (y * width + x) * 4;
rgba[offset] = intensity;
rgba[offset + 1] = intensity;
rgba[offset + 2] = intensity;
for (var x = startColumn; x < columnEnd; x++) {
values[y * width + x] = intensity;
}
}
}