diff --git a/Machines/Apple/AppleIIgs/Sound.cpp b/Machines/Apple/AppleIIgs/Sound.cpp
index d7c12fb9c..5c52d0ed9 100644
--- a/Machines/Apple/AppleIIgs/Sound.cpp
+++ b/Machines/Apple/AppleIIgs/Sound.cpp
@@ -60,9 +60,14 @@ void GLU::EnsoniqState::set_register(uint16_t address, uint8_t value) {
 		case 0x80:
 			oscillators[address & 0x1f].address = value;
 		break;
-		case 0xa0:
+		case 0xa0: {
 			oscillators[address & 0x1f].control = value;
-		break;
+
+			// Halt + M0 => reset position.
+			if((oscillators[address & 0x1f].control & 0x3) == 3) {
+				oscillators[address & 0x1f].control |= 1;
+			}
+		} break;
 		case 0xc0:
 			oscillators[address & 0x1f].table_size = value;
 		break;
@@ -199,8 +204,16 @@ void GLU::generate_audio(size_t number_of_samples, std::int16_t *target, int16_t
 					assert(false);
 				break;
 
-				case 6:	// Swap mode.
-					assert(false);
+				case 6:	// Swap mode; possibly trigger partner, and update sample.
+					// TODO: possibly this function argues in favour of summing the output
+					// in a separate loop?
+					if(remote_.oscillators[c].position & 0xff000000) {
+						remote_.oscillators[c].control |= 1;
+						remote_.oscillators[c].position = 0;
+						remote_.oscillators[c^1].control &= ~1;
+					} else {
+						output += remote_.oscillators[c].output(remote_.ram_);
+					}
 				break;
 			}
 		}
@@ -238,8 +251,16 @@ uint8_t GLU::EnsoniqState::Oscillator::sample(uint8_t *ram) {
 }
 
 int16_t GLU::EnsoniqState::Oscillator::output(uint8_t *ram) {
+	const auto level = sample(ram);
+
+	// "An oscillator will halt when a zero is encountered in its waveform table."
+	if(!level) {
+		control |= 1;
+		return 0;
+	}
+
 	// Samples are unsigned 8-bit; do the proper work to make volume work correctly.
-	return int8_t(sample(ram) ^ 128) * volume;
+	return int8_t(level ^ 128) * volume;
 }
 
 void GLU::skip_audio(EnsoniqState &state, size_t number_of_samples) {