diff --git a/Core/MMC5Audio.h b/Core/MMC5Audio.h
index 2771bdf9..976ddab3 100644
--- a/Core/MMC5Audio.h
+++ b/Core/MMC5Audio.h
@@ -76,7 +76,9 @@ protected:
 			_square2.TickEnvelope();
 		}
 
-		int16_t summedOutput = (_square1.GetOutput() + _square2.GetOutput()) * 4 + _pcmOutput;
+		//"The sound output of the square channels are equivalent in volume to the corresponding APU channels"
+		//"The polarity of all MMC5 channels is reversed compared to the APU."
+		int16_t summedOutput = -(_square1.GetOutput() + _square2.GetOutput() + _pcmOutput);
 		if(summedOutput != _lastOutput) {
 			APU::AddExpansionAudioDelta(AudioChannel::MMC5, summedOutput - _lastOutput);
 			_lastOutput = summedOutput;
diff --git a/Core/SoundMixer.cpp b/Core/SoundMixer.cpp
index c9426c1b..de6cb0b0 100644
--- a/Core/SoundMixer.cpp
+++ b/Core/SoundMixer.cpp
@@ -206,7 +206,7 @@ int16_t SoundMixer::GetOutputVolume(bool forRightChannel)
 	
 	return (int16_t)(squareVolume + tndVolume +
 		GetChannelOutput(AudioChannel::FDS, forRightChannel) * 20 +
-		GetChannelOutput(AudioChannel::MMC5, forRightChannel) * 40 +
+		GetChannelOutput(AudioChannel::MMC5, forRightChannel) * 43 +
 		GetChannelOutput(AudioChannel::Namco163, forRightChannel) * 20 +
 		GetChannelOutput(AudioChannel::Sunsoft5B, forRightChannel) * 15 +
 		GetChannelOutput(AudioChannel::VRC6, forRightChannel) * 75 +