SPU: Do DC filtering with float samples

pcsx2/SPU2/Mixer.cpp

@@ -519,20 +519,6 @@ static __forceinline StereoOut32 MixCore(const uint coreidx, const VoiceMixSet&
 	return TD + ApplyVolume(RV, thiscore.FxVol);
 }
 
-static StereoOut32 DCFilter(StereoOut32 input)
-{
-	// A simple DC blocking high-pass filter
-	// Implementation from http://peabody.sapp.org/class/dmp2/lab/dcblock/
-	// The magic number 0x7f5c is ceil(INT16_MAX * 0.995)
-	StereoOut32 output;
-	output.Left = (input.Left - DCFilterIn.Left + clamp_mix((0x7f5c * DCFilterOut.Left) >> 15));
-	output.Right = (input.Right - DCFilterIn.Right + clamp_mix((0x7f5c * DCFilterOut.Right) >> 15));
-
-	DCFilterIn = input;
-	DCFilterOut = output;
-	return output;
-}
-
 void spu2Mix()
 {
 	// Note: Playmode 4 is SPDIF, which overrides other inputs.
@@ -591,13 +577,6 @@ void spu2Mix()
 		Out = ApplyVolume(clamp_mix(Out), Cores[1].MasterVol);
 	}
 
-	// For a long time PCSX2 has had its output volume halved by
-	// an incorrect function for applying the master volume above.
-	//
-	// Adjust volume here so it matches what people have come to expect.
-	Out = ApplyVolume(Out, {0x4fff, 0x4fff});
-	Out = DCFilter(Out);
-
 #ifdef PCSX2_DEVBUILD
 	// Log final output to wavefile.
 	WaveDump::WriteCore(1, CoreSrc_External, Out);

pcsx2/SPU2/defs.h

@@ -569,8 +569,6 @@ extern u16 OutPos;
 extern u16 InputPos;
 // SPU Mixing Cycles ("Ticks mixed" counter)
 extern u32 Cycles;
-// DC Filter state
-extern StereoOut32 DCFilterIn, DCFilterOut;
 
 extern s16 spu2regs[0x010000 / sizeof(s16)];
 extern s16 _spu2mem[0x200000 / sizeof(s16)];

pcsx2/SPU2/spu2.cpp

@@ -36,6 +36,8 @@ static u32 s_current_chunk_pos;
 static u32 s_standard_volume = 0;
 static u32 s_fast_forward_volume = 0;
 
+float DCFilterIn[2], DCFilterOut[2];
+
 u32 SPU2::GetConsoleSampleRate()
 {
 	return s_psxmode ? PSX_SAMPLE_RATE : SAMPLE_RATE;
@@ -232,6 +234,9 @@ void SPU2::InternalReset(bool psxmode)
 		memset(_spu2mem + 0x2800, 7, 0x10); // from BIOS reversal. Locks the voices so they don't run free.
 		memset(_spu2mem + 0xe870, 7, 0x10); // Loop which gets left over by the BIOS, Megaman X7 relies on it being there.
 
+		memset(DCFilterIn, 0, sizeof(DCFilterIn));
+		memset(DCFilterOut, 0, sizeof(DCFilterOut));
+
 		Spdif.Info = 0; // Reset IRQ Status if it got set in a previously run game
 
 		Cores[0].Init(0);
@@ -484,11 +489,36 @@ s32 SPU2freeze(FreezeAction mode, freezeData* data)
 	return 0;
 }
 
+static void DCFilter(float *input)
+{
+	// A simple DC blocking high-pass filter
+	// Implementation from http://peabody.sapp.org/class/dmp2/lab/dcblock/
+	float output[2];
+	output[0] = (input[0] - DCFilterIn[0] + ((0.995f * DCFilterOut[0])));
+	output[1] = (input[1] - DCFilterIn[1] + ((0.995f * DCFilterOut[1])));
+
+	DCFilterIn[0] = input[0];
+	DCFilterIn[1] = input[1];
+	DCFilterOut[0] = output[0];
+	DCFilterOut[1] = output[1];
+
+	input[0] = output[0];
+	input[1] = output[1];
+}
+
 __forceinline void spu2Output(StereoOut32 out)
 {
-	// Final clamp, take care not to exceed 16 bits from here on
-	s_current_chunk[s_current_chunk_pos++] = static_cast<float>(clamp_mix(out.Left)) / INT16_MAX;
-	s_current_chunk[s_current_chunk_pos++] = static_cast<float>(clamp_mix(out.Right)) / INT16_MAX;
+	float conv[2];
+
+	conv[0] = static_cast<float>(clamp_mix(out.Left)) / INT16_MAX;
+	conv[1] = static_cast<float>(clamp_mix(out.Right)) / INT16_MAX;
+
+	/* Some games pause voices with the volume left on leaving us with
+     * significant DC offset, so we filter it out (e.x. SSX 3)*/
+	DCFilter(conv);
+
+	s_current_chunk[s_current_chunk_pos++] = conv[0];
+	s_current_chunk[s_current_chunk_pos++] = conv[1];
 	if (s_current_chunk_pos == s_current_chunk.size())
 	{
 		s_current_chunk_pos = 0;

pcsx2/SPU2/spu2sys.cpp

@@ -26,7 +26,6 @@ V_CoreDebug DebugCores[2];
 V_Core Cores[2];
 V_SPDIF Spdif;
 
-StereoOut32 DCFilterIn, DCFilterOut;
 u16 OutPos;
 u16 InputPos;
 u32 Cycles;
@@ -127,8 +126,6 @@ void V_Core::Init(int index)
 	DMAPtr = nullptr;
 	KeyOn = 0;
 	OutPos = 0;
-	DCFilterIn = {};
-	DCFilterOut = {};
 
 	psxmode = false;
 	psxSoundDataTransferControl = 0;