diff --git a/src/gba/gba-audio.c b/src/gba/gba-audio.c
index cc7acebb7..67ff89c33 100644
--- a/src/gba/gba-audio.c
+++ b/src/gba/gba-audio.c
@@ -25,6 +25,8 @@ void GBAAudioInit(struct GBAAudio* audio) {
 	audio->eventDiff = 0;
 	audio->nextSample = 0;
 	audio->sampleRate = 0x8000;
+	audio->soundcntLo = 0;
+	audio->soundcntHi = 0;
 	audio->sampleInterval = GBA_ARM7TDMI_FREQUENCY / audio->sampleRate;
 
 	CircleBufferInit(&audio->left, GBA_AUDIO_SAMPLES * sizeof(int32_t));
@@ -107,7 +109,7 @@ void GBAAudioWriteSOUND1CNT_LO(struct GBAAudio* audio, uint16_t value) {
 }
 
 void GBAAudioWriteSOUND1CNT_HI(struct GBAAudio* audio, uint16_t value) {
-	audio->ch1.wave.packed = value;
+	audio->ch1.envelope.packed = value;
 }
 
 void GBAAudioWriteSOUND1CNT_X(struct GBAAudio* audio, uint16_t value) {
@@ -115,7 +117,7 @@ void GBAAudioWriteSOUND1CNT_X(struct GBAAudio* audio, uint16_t value) {
 }
 
 void GBAAudioWriteSOUND2CNT_LO(struct GBAAudio* audio, uint16_t value) {
-	audio->ch2.wave.packed = value;
+	audio->ch2.envelope.packed = value;
 }
 
 void GBAAudioWriteSOUND2CNT_HI(struct GBAAudio* audio, uint16_t value) {
@@ -135,7 +137,7 @@ void GBAAudioWriteSOUND3CNT_X(struct GBAAudio* audio, uint16_t value) {
 }
 
 void GBAAudioWriteSOUND4CNT_LO(struct GBAAudio* audio, uint16_t value) {
-	audio->ch4.wave.packed = value;
+	audio->ch4.envelope.packed = value;
 }
 
 void GBAAudioWriteSOUND4CNT_HI(struct GBAAudio* audio, uint16_t value) {
diff --git a/src/gba/gba-audio.h b/src/gba/gba-audio.h
index 8e20582de..819b716de 100644
--- a/src/gba/gba-audio.h
+++ b/src/gba/gba-audio.h
@@ -10,15 +10,19 @@ struct GBADMA;
 
 const unsigned GBA_AUDIO_SAMPLES;
 
-union GBAAudioWave {
-	struct {
-		unsigned length : 6;
-		unsigned duty : 2;
-		unsigned stepTime : 3;
-		unsigned direction : 1;
-		unsigned initialVolume : 4;
+struct GBAAudioEnvelope {
+	union {
+		struct {
+			unsigned length : 6;
+			unsigned duty : 2;
+			unsigned stepTime : 3;
+			unsigned direction : 1;
+			unsigned initialVolume : 4;
+		};
+		uint16_t packed;
 	};
-	uint16_t packed;
+	int currentVolume;
+	int32_t nextStep;
 };
 
 union GBAAudioSquareControl {
@@ -42,12 +46,12 @@ struct GBAAudioChannel1 {
 		uint16_t packed;
 	} sweep;
 
-	union GBAAudioWave wave;
+	struct GBAAudioEnvelope envelope;
 	union GBAAudioSquareControl control;
 };
 
 struct GBAAudioChannel2 {
-	union GBAAudioWave wave;
+	struct GBAAudioEnvelope envelope;
 	union GBAAudioSquareControl control;
 };
 
@@ -86,7 +90,7 @@ struct GBAAudioChannel3 {
 };
 
 struct GBAAudioChannel4 {
-	union GBAAudioWave wave;
+	struct GBAAudioEnvelope envelope;
 	union {
 		struct {
 			unsigned ratio : 3;