From e9ec009836d9501909a519fc94b52d09c2ad6ddd Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Wed, 7 Dec 2022 01:21:21 -0800
Subject: [PATCH] GB Audio: Fix channel 3 volume being changed between samples
 (fixes #1896)

---
 CHANGES        |  1 +
 src/gb/audio.c | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/CHANGES b/CHANGES
index 73b36504c..07d262ca1 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,7 @@ Features:
  - Debugger: Add range watchpoints
 Emulation fixes:
  - GB Audio: Fix channels 1/2 not playing when resetting volume (fixes mgba.io/i/2614)
+ - GB Audio: Fix channel 3 volume being changed between samples (fixes mgba.io/i/1896)
  - GB Serialize: Don't write BGP/OBP when loading SCGB state (fixes mgba.io/i/2694)
  - GB SIO: Further fix bidirectional transfer starting
  - GBA: Fix resetting key IRQ state (fixes mgba.io/i/2716)
diff --git a/src/gb/audio.c b/src/gb/audio.c
index 26675a983..516c6c663 100644
--- a/src/gb/audio.c
+++ b/src/gb/audio.c
@@ -269,6 +269,29 @@ void GBAudioWriteNR31(struct GBAudio* audio, uint8_t value) {
 void GBAudioWriteNR32(struct GBAudio* audio, uint8_t value) {
 	GBAudioRun(audio, mTimingCurrentTime(audio->timing), 0x4);
 	audio->ch3.volume = GBAudioRegisterBankVolumeGetVolumeGB(value);
+
+	audio->ch3.sample = audio->ch3.wavedata8[audio->ch3.window >> 1];
+	if (!(audio->ch3.window & 1)) {
+		audio->ch3.sample >>= 4;
+	}
+	audio->ch3.sample &= 0xF;
+	int volume;
+	switch (audio->ch3.volume) {
+	case 0:
+		volume = 4;
+		break;
+	case 1:
+		volume = 0;
+		break;
+	case 2:
+		volume = 1;
+		break;
+	default:
+	case 3:
+		volume = 2;
+		break;
+	}
+	audio->ch3.sample >>= volume;
 }
 
 void GBAudioWriteNR33(struct GBAudio* audio, uint8_t value) {