fix(analysis): detect full-band spectral cutoff

lib/l10n/app_localizations.dart

@@ -5936,6 +5936,12 @@ abstract class AppLocalizations {
   /// **'Spectral Cutoff'**
   String get audioAnalysisSpectralCutoff;
 
+  /// Displayed when no reliable broadband spectral cutoff can be detected
+  ///
+  /// In en, this message translates to:
+  /// **'Not detected'**
+  String get audioAnalysisCutoffNotDetected;
+
   /// Per-channel audio analysis section label
   ///
   /// In en, this message translates to:

lib/l10n/app_localizations_de.dart

@@ -3597,6 +3597,9 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get audioAnalysisSpectralCutoff => 'Spektralschnitt';
 
+  @override
+  String get audioAnalysisCutoffNotDetected => 'Not detected';
+
   @override
   String get audioAnalysisChannelStats => 'Pro Kanal Statistik';
 

lib/l10n/app_localizations_en.dart

@@ -3555,6 +3555,9 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get audioAnalysisSpectralCutoff => 'Spectral Cutoff';
 
+  @override
+  String get audioAnalysisCutoffNotDetected => 'Not detected';
+
   @override
   String get audioAnalysisChannelStats => 'Per-channel Stats';
 

lib/l10n/app_localizations_es.dart

@@ -3555,6 +3555,9 @@ class AppLocalizationsEs extends AppLocalizations {
   @override
   String get audioAnalysisSpectralCutoff => 'Spectral Cutoff';
 
+  @override
+  String get audioAnalysisCutoffNotDetected => 'Not detected';
+
   @override
   String get audioAnalysisChannelStats => 'Per-channel Stats';
 

lib/l10n/app_localizations_fr.dart

@@ -3648,6 +3648,9 @@ class AppLocalizationsFr extends AppLocalizations {
   @override
   String get audioAnalysisSpectralCutoff => 'Limite spectrale';
 
+  @override
+  String get audioAnalysisCutoffNotDetected => 'Not detected';
+
   @override
   String get audioAnalysisChannelStats => 'Statistiques par chaîne';
 

lib/l10n/app_localizations_id.dart

@@ -3552,6 +3552,9 @@ class AppLocalizationsId extends AppLocalizations {
   @override
   String get audioAnalysisSpectralCutoff => 'Spectral Cutoff';
 
+  @override
+  String get audioAnalysisCutoffNotDetected => 'Tidak terdeteksi';
+
   @override
   String get audioAnalysisChannelStats => 'Per-channel Stats';
 

lib/l10n/app_localizations_ja.dart

@@ -3544,6 +3544,9 @@ class AppLocalizationsJa extends AppLocalizations {
   @override
   String get audioAnalysisSpectralCutoff => 'Spectral Cutoff';
 
+  @override
+  String get audioAnalysisCutoffNotDetected => 'Not detected';
+
   @override
   String get audioAnalysisChannelStats => 'Per-channel Stats';
 

lib/l10n/app_localizations_ko.dart

@@ -3453,6 +3453,9 @@ class AppLocalizationsKo extends AppLocalizations {
   @override
   String get audioAnalysisSpectralCutoff => '주파수 컷오프';
 
+  @override
+  String get audioAnalysisCutoffNotDetected => 'Not detected';
+
   @override
   String get audioAnalysisChannelStats => '채널별 통계';
 

lib/l10n/app_localizations_pt.dart

@@ -3555,6 +3555,9 @@ class AppLocalizationsPt extends AppLocalizations {
   @override
   String get audioAnalysisSpectralCutoff => 'Spectral Cutoff';
 
+  @override
+  String get audioAnalysisCutoffNotDetected => 'Not detected';
+
   @override
   String get audioAnalysisChannelStats => 'Per-channel Stats';
 

lib/l10n/app_localizations_ru.dart

@@ -3584,6 +3584,9 @@ class AppLocalizationsRu extends AppLocalizations {
   @override
   String get audioAnalysisSpectralCutoff => 'Spectral Cutoff';
 
+  @override
+  String get audioAnalysisCutoffNotDetected => 'Not detected';
+
   @override
   String get audioAnalysisChannelStats => 'Per-channel Stats';
 

lib/l10n/app_localizations_tr.dart

@@ -3585,6 +3585,9 @@ class AppLocalizationsTr extends AppLocalizations {
   @override
   String get audioAnalysisSpectralCutoff => 'Spectral Cutoff';
 
+  @override
+  String get audioAnalysisCutoffNotDetected => 'Not detected';
+
   @override
   String get audioAnalysisChannelStats => 'Per-channel Stats';
 

lib/l10n/app_localizations_uk.dart

@@ -3600,6 +3600,9 @@ class AppLocalizationsUk extends AppLocalizations {
   @override
   String get audioAnalysisSpectralCutoff => 'Spectral Cutoff';
 
+  @override
+  String get audioAnalysisCutoffNotDetected => 'Not detected';
+
   @override
   String get audioAnalysisChannelStats => 'Per-channel Stats';
 

lib/l10n/arb/app_en.arb

@@ -4577,6 +4577,10 @@
   "@audioAnalysisSpectralCutoff": {
     "description": "Estimated spectral cutoff metric label"
   },
+  "audioAnalysisCutoffNotDetected": "Not detected",
+  "@audioAnalysisCutoffNotDetected": {
+    "description": "Displayed when no reliable broadband spectral cutoff can be detected"
+  },
   "audioAnalysisChannelStats": "Per-channel Stats",
   "@audioAnalysisChannelStats": {
     "description": "Per-channel audio analysis section label"

lib/l10n/arb/app_id.arb

@@ -3432,6 +3432,7 @@
     "description": "Cache item title for local library cover art images"
   },
   "audioAnalysisSpectralCutoff": "Spectral Cutoff",
+  "audioAnalysisCutoffNotDetected": "Tidak terdeteksi",
   "dialogDelete": "Hapus",
   "@dialogDelete": {
     "description": "Dialog button - delete item"

lib/widgets/audio_analysis_info_card.dart

@@ -171,13 +171,16 @@ class _AudioInfoCard extends StatelessWidget {
                   value: _formatClipping(context, data.clippingSamples),
                   cs: cs,
                 ),
-                if (data.spectralCutoffHz != null)
-                  _MetricChip(
-                    icon: Icons.filter_alt_outlined,
-                    label: context.l10n.audioAnalysisSpectralCutoff,
-                    value: _formatFrequency(data.spectralCutoffHz!),
-                    cs: cs,
+                _MetricChip(
+                  icon: Icons.filter_alt_outlined,
+                  label: context.l10n.audioAnalysisSpectralCutoff,
+                  value: formatAudioAnalysisSpectralCutoff(
+                    data.spectralCutoffHz,
+                    notDetectedLabel:
+                        context.l10n.audioAnalysisCutoffNotDetected,
                   ),
+                  cs: cs,
+                ),
                 _MetricChip(
                   icon: Icons.numbers,
                   label: context.l10n.audioAnalysisSamples,
@@ -228,11 +231,6 @@ class _AudioInfoCard extends StatelessWidget {
     return data.channels > 0 ? '${data.channels}' : 'N/A';
   }
 
-  String _formatFrequency(double hz) {
-    if (hz >= 1000) return '${(hz / 1000).toStringAsFixed(1)} kHz';
-    return '${hz.round()} Hz';
-  }
-
   String _formatBitrate(int bitsPerSecond) {
     if (bitsPerSecond >= 1000000) {
       return '${(bitsPerSecond / 1000000).toStringAsFixed(2)} Mbps';

lib/widgets/audio_analysis_models.dart

@@ -3,7 +3,7 @@ part of 'audio_analysis_widget.dart';
 // Analysis result models and per-run parameter records.
 
 class AudioAnalysisData {
-  static const cacheVersion = 7;
+  static const cacheVersion = 8;
 
   final String filePath;
   final int fileSize;

lib/widgets/audio_analysis_widget.dart

@@ -24,6 +24,19 @@ const int audioSpectrogramHeight = 800;
 const int audioSpectralAnalysisWidth = 400;
 const double audioSpectrogramDynamicRangeDb = 120;
 
+String formatAudioAnalysisSpectralCutoff(
+  double? cutoffHz, {
+  required String notDetectedLabel,
+}) {
+  if (cutoffHz == null || !cutoffHz.isFinite || cutoffHz <= 0) {
+    return notDetectedLabel;
+  }
+  if (cutoffHz >= 1000) {
+    return '${(cutoffHz / 1000).toStringAsFixed(1)} kHz';
+  }
+  return '${cutoffHz.round()} Hz';
+}
+
 String _buildShowspectrumOptions({required int width, required String color}) {
   return 'showspectrumpic='
       's=${width}x$audioSpectrogramHeight:'
@@ -385,8 +398,10 @@ double? estimateEffectiveSpectralCutoffHz({
   }
 
   // A genuinely broadband signal with no internal falling edge reaches the
-  // analysis ceiling. Report Nyquist only when both its baseband and top band
-  // are populated; silence or an isolated high-frequency line returns null.
+  // analysis ceiling. Natural music has a pronounced spectral tilt, so the
+  // top band does not need to be almost as loud as the baseband. It must still
+  // sit clearly above the measured low-level floor; silence or an isolated
+  // high-frequency line therefore continues to return null.
   final basebandLevel = _spectralMedian(
     smoothed,
     (height * 0.05).floor(),
@@ -397,7 +412,8 @@ double? estimateEffectiveSpectralCutoffHz({
     (height * 0.90).floor(),
     math.max(1, (height * 0.98).floor()),
   );
-  if (basebandLevel >= 24 && topBandLevel >= basebandLevel - minimumDrop) {
+  final populatedTopFloor = math.max(24.0, lowLevel * 0.60);
+  if (basebandLevel >= 24 && topBandLevel >= populatedTopFloor) {
     return maxFrequencyHz;
   }
   return null;

test/audio_analysis_info_card_test.dart

@@ -0,0 +1,26 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:spotiflac_android/widgets/audio_analysis_widget.dart';
+
+void main() {
+  group('spectral cutoff formatting', () {
+    test('formats a detected cutoff frequency', () {
+      expect(
+        formatAudioAnalysisSpectralCutoff(
+          22605,
+          notDetectedLabel: 'Not detected',
+        ),
+        '22.6 kHz',
+      );
+    });
+
+    test('keeps the metric visible when no cutoff is detected', () {
+      expect(
+        formatAudioAnalysisSpectralCutoff(
+          null,
+          notDetectedLabel: 'Not detected',
+        ),
+        'Not detected',
+      );
+    });
+  });
+}

test/audio_analysis_spectrogram_test.dart

@@ -250,6 +250,30 @@ lavfi.r128.true_peak=0.907
       expect(cutoff, nyquist);
     });
 
+    test(
+      'reports Nyquist for full-band music with a natural spectral tilt',
+      () {
+        const cdNyquist = 22050.0;
+        final intensity = _blankIntensity(width, height);
+        _paintNaturalSpectralTilt(
+          intensity,
+          width: width,
+          height: height,
+          lowFrequencyIntensity: 140,
+          nyquistIntensity: 26,
+        );
+
+        final cutoff = estimateEffectiveSpectralCutoffHz(
+          intensity: intensity,
+          width: width,
+          height: height,
+          maxFrequencyHz: cdNyquist,
+        );
+
+        expect(cutoff, cdNyquist);
+      },
+    );
+
     test('does not report an isolated line as a broadband cutoff', () {
       final intensity = _blankIntensity(width, height);
       _paintFrequencyBand(
@@ -312,3 +336,24 @@ void _paintFrequencyBand(
     }
   }
 }
+
+void _paintNaturalSpectralTilt(
+  Uint8List values, {
+  required int width,
+  required int height,
+  required int lowFrequencyIntensity,
+  required int nyquistIntensity,
+}) {
+  final span = lowFrequencyIntensity - nyquistIntensity;
+  for (var y = 0; y < height; y++) {
+    final normalizedFrequency = (height - y - 0.5) / height;
+    final intensity =
+        (lowFrequencyIntensity -
+                span * normalizedFrequency * normalizedFrequency)
+            .round()
+            .clamp(0, 255);
+    for (var x = 0; x < width; x++) {
+      values[y * width + x] = intensity;
+    }
+  }
+}