From 0dbe178e7fba2ca4dbd430653fb7b019b9453171 Mon Sep 17 00:00:00 2001
From: "Brandon McGinty (chatgpt)" <git@bmcginty.us>
Date: Sun, 9 Aug 2026 20:29:02 -0400
Subject: [PATCH] Check local Mumble audio fidelity

---
 gumble/gumble/integration_audio_test.go   | 28 +++-----------
 gumble/gumble/integration_quality_test.go | 45 +++++++++++++++++++++++
 2 files changed, 51 insertions(+), 22 deletions(-)
 create mode 100644 gumble/gumble/integration_quality_test.go

diff --git a/gumble/gumble/integration_audio_test.go b/gumble/gumble/integration_audio_test.go
index 10da40a..8355309 100644
--- a/gumble/gumble/integration_audio_test.go
+++ b/gumble/gumble/integration_audio_test.go
@@ -82,34 +82,18 @@ func TestLocalMumbleAudioRoundTrip(t *testing.T) {
 	}
 	select {
 	case packet = <-listener.packets:
-		peak := 0
-		crossings := 0
-		previous := 0
-		// The decoder returns interleaved stereo; inspect one channel. A rising
-		// zero-crossing estimate verifies the 440 Hz source survived Opus rather
-		// than merely proving that arbitrary non-silent audio was relayed.
-		for i := 0; i < len(packet.AudioBuffer); i += gumble.AudioChannels {
-			v := int(packet.AudioBuffer[i])
-			if v < 0 {
-				if -v > peak {
-					peak = -v
-				}
-			} else if v > peak {
-				peak = v
-			}
-			if previous <= 0 && v > 0 {
-				crossings++
-			}
-			previous = v
-		}
+		frequency, purity, peak := audioQuality(packet.AudioBuffer)
 		if peak < 500 {
 			t.Fatalf("received silent audio peak=%d", peak)
 		}
-		samples := len(packet.AudioBuffer) / gumble.AudioChannels
-		frequency := float64(crossings*gumble.AudioSampleRate) / float64(samples)
 		if math.Abs(frequency-440) > 120 {
 			t.Fatalf("received frequency %.1f Hz, want generated 440 Hz", frequency)
 		}
+		// A clean sine projects strongly onto its fundamental. This detects
+		// severe codec distortion beyond simple packet arrival and pitch checks.
+		if purity < 0.65 {
+			t.Fatalf("received audio is distorted: 440 Hz purity=%.2f", purity)
+		}
 	case <-time.After(8 * time.Second):
 		t.Fatal("timed out waiting for relayed audio")
 	}
diff --git a/gumble/gumble/integration_quality_test.go b/gumble/gumble/integration_quality_test.go
new file mode 100644
index 0000000..aa7e383
--- /dev/null
+++ b/gumble/gumble/integration_quality_test.go
@@ -0,0 +1,45 @@
+//go:build integration
+
+package gumble_test
+
+import (
+	"math"
+
+	"git.stormux.org/storm/barnard/gumble/gumble"
+)
+
+// audioQuality returns the rising-crossing pitch estimate, the fraction of
+// RMS energy explained by the 440 Hz fundamental, and the sample peak.
+func audioQuality(audio gumble.AudioBuffer) (frequency, purity float64, peak int) {
+	if len(audio) < gumble.AudioChannels {
+		return 0, 0, 0
+	}
+	samples := len(audio) / gumble.AudioChannels
+	crossings, previous := 0, 0
+	var energy, sine, cosine float64
+	for i := 0; i < samples; i++ {
+		value := int(audio[i*gumble.AudioChannels])
+		if value < 0 {
+			if -value > peak {
+				peak = -value
+			}
+		} else if value > peak {
+			peak = value
+		}
+		if previous <= 0 && value > 0 {
+			crossings++
+		}
+		previous = value
+		x := float64(value)
+		phase := 2 * math.Pi * 440 * float64(i) / gumble.AudioSampleRate
+		energy += x * x
+		sine += x * math.Sin(phase)
+		cosine += x * math.Cos(phase)
+	}
+	frequency = float64(crossings*gumble.AudioSampleRate) / float64(samples)
+	if energy != 0 {
+		// Projection amplitude divided by RMS, normalized for sine RMS.
+		purity = math.Sqrt(2) * math.Hypot(sine, cosine) / math.Sqrt(energy*float64(samples))
+	}
+	return
+}