Give the audio quality rules a single home

AudioQualityEnhancer.Tests/AudioQualityThresholdsTests.cs

@@ -0,0 +1,113 @@
+using AudioQualityEnhancer.Models;
+using AudioQualityEnhancer.Services;
+
+namespace AudioQualityEnhancer.Tests;
+
+public sealed class AudioQualityThresholdsTests
+{
+    [Theory]
+    [InlineData(true, 1, 95_000, true)]
+    [InlineData(true, 1, 96_000, false)]
+    [InlineData(true, 2, 127_000, true)]
+    [InlineData(true, 2, 128_000, false)]
+    [InlineData(true, 2, 96_000, true)]
+    [InlineData(false, 2, 64_000, false)]
+    [InlineData(true, 2, 0, false)]
+    public void HasLowBitrate_UsesAChannelDependentThreshold(bool isLossy, int channels, int bitRate, bool expected)
+    {
+        using var info = new AudioInfo
+        {
+            IsLikelyLossy = isLossy,
+            Channels = channels,
+            BitRate = bitRate
+        };
+
+        Assert.Equal(expected, AudioQualityThresholds.HasLowBitrate(info));
+    }
+
+    /// <summary>A lossless source is never judged by its bitrate.</summary>
+    [Fact]
+    public void HasLowBitrate_IgnoresALosslessSource()
+    {
+        using var info = new AudioInfo { IsLikelyLossy = false, Channels = 2, BitRate = 1_000 };
+
+        Assert.False(AudioQualityThresholds.HasLowBitrate(info));
+    }
+
+    [Fact]
+    public void HasLowBitrate_IsFalseWithoutInfo()
+    {
+        Assert.False(AudioQualityThresholds.HasLowBitrate(null));
+    }
+
+    [Theory]
+    [InlineData(0, false)]
+    [InlineData(22_050, true)]
+    [InlineData(31_999, true)]
+    [InlineData(32_000, false)]
+    [InlineData(48_000, false)]
+    public void HasLowSampleRate_UsesTheDocumentedBoundary(int sampleRate, bool expected)
+    {
+        using var info = new AudioInfo { SampleRate = sampleRate };
+
+        Assert.Equal(expected, AudioQualityThresholds.HasLowSampleRate(info));
+    }
+
+    [Theory]
+    [InlineData(-2.0, false)]
+    [InlineData(-1.1, false)]
+    [InlineData(-1.0, true)]
+    [InlineData(-0.5, true)]
+    public void HasLowHeadroom_UsesTheDocumentedBoundary(double truePeakDb, bool expected)
+    {
+        using var diagnostics = new AudioDiagnostics { TruePeakDb = truePeakDb };
+
+        Assert.Equal(expected, AudioQualityThresholds.HasLowHeadroom(diagnostics));
+    }
+
+    [Fact]
+    public void HasLowHeadroom_FallsBackToTheMeasuredMaximum()
+    {
+        using var diagnostics = new AudioDiagnostics { TruePeakDb = null, MaxVolumeDb = -0.2 };
+
+        Assert.True(AudioQualityThresholds.HasLowHeadroom(diagnostics));
+    }
+
+    /// <summary>
+    /// Clipping is reported on its own, so it must not also count as low headroom or the
+    /// same problem would appear twice in the findings.
+    /// </summary>
+    [Fact]
+    public void HasLowHeadroom_ExcludesActualClipping()
+    {
+        using var diagnostics = new AudioDiagnostics { TruePeakDb = 0.5, MaxVolumeDb = 0.5 };
+
+        Assert.True(AudioQualityThresholds.HasPotentialClipping(diagnostics));
+        Assert.False(AudioQualityThresholds.HasLowHeadroom(diagnostics));
+    }
+
+    [Theory]
+    [InlineData(-30.0, true, false)]
+    [InlineData(-28.0, false, false)]
+    [InlineData(-16.0, false, false)]
+    [InlineData(-9.0, false, false)]
+    [InlineData(-5.0, false, true)]
+    public void LoudnessBands_DoNotOverlap(double lufs, bool veryQuiet, bool alreadyLoud)
+    {
+        using var diagnostics = new AudioDiagnostics { IntegratedLoudnessLufs = lufs };
+
+        Assert.Equal(veryQuiet, AudioQualityThresholds.IsVeryQuiet(diagnostics));
+        Assert.Equal(alreadyLoud, AudioQualityThresholds.IsAlreadyLoud(diagnostics));
+        Assert.Equal(veryQuiet || alreadyLoud, AudioQualityThresholds.HasProblematicLoudness(diagnostics));
+    }
+
+    [Fact]
+    public void AllChecks_AreFalseWithoutDiagnostics()
+    {
+        Assert.False(AudioQualityThresholds.HasPotentialClipping(null));
+        Assert.False(AudioQualityThresholds.HasLowHeadroom(null));
+        Assert.False(AudioQualityThresholds.IsVeryQuiet(null));
+        Assert.False(AudioQualityThresholds.IsAlreadyLoud(null));
+        Assert.False(AudioQualityThresholds.HasProblematicLoudness(null));
+    }
+}

Services/AudioAnalysisInsightService.cs

@@ -19,18 +19,14 @@ public AudioAnalysisReport BuildReport(AudioInfo info, AudioDiagnostics? diagnos
             AddRecommendation(recommendations, AudioAnalysisFindingKind.LossyTranscodingRisk);
         }
 
-        if (info.IsLikelyLossy && info.BitRate is > 0)
+        if (AudioQualityThresholds.HasLowBitrate(info))
         {
-            var lowBitrateThreshold = info.Channels == 1 ? 96_000 : 128_000;
-            if (info.BitRate.Value < lowBitrateThreshold)
-            {
-                score -= 15;
-                AddFinding(findings, AudioAnalysisFindingKind.LowBitrate, AudioInsightSeverity.Warning);
-                AddRecommendation(recommendations, AudioAnalysisFindingKind.LowBitrate);
-            }
+            score -= 15;
+            AddFinding(findings, AudioAnalysisFindingKind.LowBitrate, AudioInsightSeverity.Warning);
+            AddRecommendation(recommendations, AudioAnalysisFindingKind.LowBitrate);
         }
 
-        if (info.SampleRate is > 0 and < 32000)
+        if (AudioQualityThresholds.HasLowSampleRate(info))
         {
             score -= 10;
             AddFinding(findings, AudioAnalysisFindingKind.LowSampleRate, AudioInsightSeverity.Warning);
@@ -56,27 +52,26 @@ public AudioAnalysisReport BuildReport(AudioInfo info, AudioDiagnostics? diagnos
         }
         else
         {
-            var peak = diagnostics.TruePeakDb ?? diagnostics.MaxVolumeDb;
-            if (diagnostics.HasPotentialClipping)
+            if (AudioQualityThresholds.HasPotentialClipping(diagnostics))
             {
                 score -= 25;
                 AddFinding(findings, AudioAnalysisFindingKind.PotentialClipping, AudioInsightSeverity.Critical);
                 AddRecommendation(recommendations, AudioAnalysisFindingKind.PotentialClipping);
             }
-            else if (peak is >= -1.0)
+            else if (AudioQualityThresholds.HasLowHeadroom(diagnostics))
             {
                 score -= 10;
                 AddFinding(findings, AudioAnalysisFindingKind.LowHeadroom, AudioInsightSeverity.Warning);
                 AddRecommendation(recommendations, AudioAnalysisFindingKind.LowHeadroom);
             }
 
-            if (diagnostics.IntegratedLoudnessLufs is < -28)
+            if (AudioQualityThresholds.IsVeryQuiet(diagnostics))
             {
                 score -= 10;
                 AddFinding(findings, AudioAnalysisFindingKind.VeryQuiet, AudioInsightSeverity.Warning);
                 AddRecommendation(recommendations, AudioAnalysisFindingKind.VeryQuiet);
             }
-            else if (diagnostics.IntegratedLoudnessLufs is > -9)
+            else if (AudioQualityThresholds.IsAlreadyLoud(diagnostics))
             {
                 score -= 10;
                 AddFinding(findings, AudioAnalysisFindingKind.AlreadyLoud, AudioInsightSeverity.Warning);

Services/AudioProfileAdvisorService.cs

@@ -19,14 +19,14 @@ public AudioProfileAdvice BuildAdvice(AudioInfo? info, AudioDiagnostics? diagnos
         }
 
         var suggestions = new Dictionary<string, AudioProfileSuggestion>(StringComparer.Ordinal);
-        var hasLowBitrate = HasLowBitrate(info);
-        var hasLowSampleRate = info.SampleRate is > 0 and < 32000;
+        var hasLowBitrate = AudioQualityThresholds.HasLowBitrate(info);
+        var hasLowSampleRate = AudioQualityThresholds.HasLowSampleRate(info);
         var looksSpeechLike = info.Channels == 1 || hasLowBitrate || hasLowSampleRate;
         var isVideoSource = IsVideoSource(info);
         var hasAdvancedDiagnostics = diagnostics is not null;
-        var hasPotentialClipping = diagnostics?.HasPotentialClipping == true;
-        var hasLowHeadroom = !hasPotentialClipping && (diagnostics?.TruePeakDb ?? diagnostics?.MaxVolumeDb) is >= -1.0;
-        var hasProblematicLoudness = diagnostics?.IntegratedLoudnessLufs is < -28 or > -9;
+        var hasPotentialClipping = AudioQualityThresholds.HasPotentialClipping(diagnostics);
+        var hasLowHeadroom = AudioQualityThresholds.HasLowHeadroom(diagnostics);
+        var hasProblematicLoudness = AudioQualityThresholds.HasProblematicLoudness(diagnostics);
         var hasTechnicalWarnings = info.IsLikelyLossy || hasLowBitrate || hasLowSampleRate || hasPotentialClipping || hasLowHeadroom || hasProblematicLoudness;
 
         if (looksSpeechLike)
@@ -159,17 +159,6 @@ private static void AddSuggestion(IDictionary<string, AudioProfileSuggestion> su
         }
     }
 
-    private static bool HasLowBitrate(AudioInfo info)
-    {
-        if (!info.IsLikelyLossy || info.BitRate is not > 0)
-        {
-            return false;
-        }
-
-        var threshold = info.Channels == 1 ? 96_000 : 128_000;
-        return info.BitRate.Value < threshold;
-    }
-
     private static bool IsVideoSource(AudioInfo info)
     {
         var extension = Path.GetExtension(info.SourcePath);

Services/AudioQualityThresholds.cs

@@ -0,0 +1,77 @@
+using AudioQualityEnhancer.Models;
+
+namespace AudioQualityEnhancer.Services;
+
+/// <summary>
+/// The rules that decide when source or output audio counts as weak. They were written
+/// out four times - in the analysis scoring, the profile advice, the result validation
+/// and the view model warnings - with the same numbers in each place, so a change to one
+/// of them would have made the interface contradict itself with nothing to catch it.
+/// </summary>
+public static class AudioQualityThresholds
+{
+    /// <summary>A mono source carries one channel, so it holds up at a lower bitrate.</summary>
+    public const int LowBitrateMonoBitsPerSecond = 96_000;
+
+    public const int LowBitrateMultiChannelBitsPerSecond = 128_000;
+
+    public const int LowSampleRateHz = 32_000;
+
+    /// <summary>Peak level from which a re-encode is likely to push samples over full scale.</summary>
+    public const double LowHeadroomPeakDb = -1.0;
+
+    public const double VeryQuietLufs = -28;
+
+    public const double AlreadyLoudLufs = -9;
+
+    /// <summary>A lossy source below the bitrate its channel count needs to hold up.</summary>
+    public static bool HasLowBitrate(AudioInfo? info)
+    {
+        if (info is null || !info.IsLikelyLossy || info.BitRate is not > 0)
+        {
+            return false;
+        }
+
+        var threshold = info.Channels == 1
+            ? LowBitrateMonoBitsPerSecond
+            : LowBitrateMultiChannelBitsPerSecond;
+
+        return info.BitRate.Value < threshold;
+    }
+
+    public static bool HasLowSampleRate(AudioInfo? info)
+    {
+        return info?.SampleRate is > 0 and < LowSampleRateHz;
+    }
+
+    public static bool HasPotentialClipping(AudioDiagnostics? diagnostics)
+    {
+        return diagnostics?.HasPotentialClipping == true;
+    }
+
+    /// <summary>
+    /// Little headroom left below full scale. Actual clipping is reported on its own and
+    /// would otherwise be reported twice, so it is excluded here.
+    /// </summary>
+    public static bool HasLowHeadroom(AudioDiagnostics? diagnostics)
+    {
+        return !HasPotentialClipping(diagnostics) &&
+               (diagnostics?.TruePeakDb ?? diagnostics?.MaxVolumeDb) is >= LowHeadroomPeakDb;
+    }
+
+    public static bool IsVeryQuiet(AudioDiagnostics? diagnostics)
+    {
+        return diagnostics?.IntegratedLoudnessLufs is < VeryQuietLufs;
+    }
+
+    /// <summary>Mutually exclusive with <see cref="IsVeryQuiet"/>, the bands do not overlap.</summary>
+    public static bool IsAlreadyLoud(AudioDiagnostics? diagnostics)
+    {
+        return diagnostics?.IntegratedLoudnessLufs is > AlreadyLoudLufs;
+    }
+
+    public static bool HasProblematicLoudness(AudioDiagnostics? diagnostics)
+    {
+        return IsVeryQuiet(diagnostics) || IsAlreadyLoud(diagnostics);
+    }
+}

Services/AudioValidationService.cs

@@ -312,12 +312,11 @@ private static void AddPeakFindings(AudioDiagnostics? outputDiagnostics, ICollec
             return;
         }
 
-        var peak = outputDiagnostics.TruePeakDb ?? outputDiagnostics.MaxVolumeDb;
-        if (outputDiagnostics.HasPotentialClipping)
+        if (AudioQualityThresholds.HasPotentialClipping(outputDiagnostics))
         {
             AddFinding(findings, AudioComparisonFindingKind.PotentialClipping, AudioInsightSeverity.Critical);
         }
-        else if (peak is >= -1.0)
+        else if (AudioQualityThresholds.HasLowHeadroom(outputDiagnostics))
         {
             AddFinding(findings, AudioComparisonFindingKind.LowHeadroom, AudioInsightSeverity.Warning);
         }

ViewModels/MainViewModel.Insights.cs

@@ -52,37 +52,33 @@ private void UpdateAnalysisWarnings()
     {
         var warnings = new List<string>();
 
-        if (AudioInfo?.IsLikelyLossy == true && AudioInfo.BitRate is > 0)
+        if (AudioQualityThresholds.HasLowBitrate(AudioInfo))
         {
-            var lowBitrateThreshold = AudioInfo.Channels == 1 ? 96_000 : 128_000;
-            if (AudioInfo.BitRate.Value < lowBitrateThreshold)
-            {
-                warnings.Add(LocalizationService.Instance.Format("Warning_LowBitrateFormat", AudioInfo.BitRateDisplay));
-            }
+            warnings.Add(LocalizationService.Instance.Format("Warning_LowBitrateFormat", AudioInfo!.BitRateDisplay));
         }
 
-        if (AudioInfo?.SampleRate is > 0 and < 32000)
+        if (AudioQualityThresholds.HasLowSampleRate(AudioInfo))
         {
-            warnings.Add(LocalizationService.Instance.Format("Warning_LowSampleRateFormat", AudioInfo.SampleRateDisplay));
+            warnings.Add(LocalizationService.Instance.Format("Warning_LowSampleRateFormat", AudioInfo!.SampleRateDisplay));
         }
 
         var diagnostics = AudioDiagnostics;
         if (diagnostics is not null)
         {
-            if (diagnostics.HasPotentialClipping)
+            if (AudioQualityThresholds.HasPotentialClipping(diagnostics))
             {
                 warnings.Add(LocalizationService.Instance["Warning_PotentialClipping"]);
             }
-            else if ((diagnostics.TruePeakDb ?? diagnostics.MaxVolumeDb) is >= -1.0)
+            else if (AudioQualityThresholds.HasLowHeadroom(diagnostics))
             {
                 warnings.Add(LocalizationService.Instance["Warning_LowHeadroom"]);
             }
 
-            if (diagnostics.IntegratedLoudnessLufs is < -28)
+            if (AudioQualityThresholds.IsVeryQuiet(diagnostics))
             {
                 warnings.Add(LocalizationService.Instance["Warning_VeryQuiet"]);
             }
-            else if (diagnostics.IntegratedLoudnessLufs is > -9)
+            else if (AudioQualityThresholds.IsAlreadyLoud(diagnostics))
             {
                 warnings.Add(LocalizationService.Instance["Warning_AlreadyLoud"]);
             }