wip gets wippier with eventual leadup to something nice

src/burn/snd/dac.cpp

@@ -30,6 +30,38 @@ static INT32 bAddSignal;
 static INT32 (*pCPUTotalCycles)() = NULL;
 static UINT32 nDACCPUMHZ = 0;
 
+// single-order dc blocking filter
+static INT32 dac_dcblock   = 0; // enable
+static INT16 dac_lastin_r  = 0;
+static INT16 dac_lastout_r = 0;
+static INT16 dac_lastin_l  = 0;
+static INT16 dac_lastout_l = 0;
+
+void DACDCBlock(INT32 enable)
+{
+    dac_dcblock = enable;
+}
+
+static INT16 dc_blockR(INT16 sam)
+{
+    if (!dac_dcblock) return sam;
+    INT16 outr = sam - dac_lastin_r + 0.998 * dac_lastout_r;
+    dac_lastin_r = sam;
+    dac_lastout_r = outr;
+
+    return outr;
+}
+
+static INT16 dc_blockL(INT16 sam)
+{
+    if (!dac_dcblock) return sam;
+    INT16 outl = sam - dac_lastin_l + 0.998 * dac_lastout_l;
+    dac_lastin_l = sam;
+    dac_lastout_l = outl;
+
+    return outl;
+}
+
 static INT32 DACSyncInternal()
 {
 	return (INT32)(float)(nBurnSoundLen * (pCPUTotalCycles() / (nDACCPUMHZ / (nBurnFPS / 100.0000))));
@@ -99,8 +131,8 @@ void DACUpdate(INT16* Buffer, INT32 Length)
 
 	if (bAddSignal) {
 		while (Length--) {
-			Buffer[0] = BURN_SND_CLIP((INT32)(lbuf[0] + Buffer[0]));
-			Buffer[1] = BURN_SND_CLIP((INT32)(rbuf[0] + Buffer[1]));
+			Buffer[0] = BURN_SND_CLIP((INT32)(dc_blockL(lbuf[0]) + Buffer[0]));
+			Buffer[1] = BURN_SND_CLIP((INT32)(dc_blockR(rbuf[0]) + Buffer[1]));
 			Buffer += 2;
 			lbuf[0] = 0; // clear buffer
 			rbuf[0] = 0; // clear buffer
@@ -109,8 +141,8 @@ void DACUpdate(INT16* Buffer, INT32 Length)
 		}
 	} else {
 		while (Length--) {
-			Buffer[0] = lbuf[0];
-			Buffer[1] = rbuf[0];
+			Buffer[0] = dc_blockL(lbuf[0]);
+			Buffer[1] = dc_blockR(rbuf[0]);
 			Buffer += 2;
 			lbuf[0] = 0; // clear buffer
 			rbuf[0] = 0; // clear buffer
@@ -181,6 +213,27 @@ void DACWrite16Stereo(INT32 Chip, INT16 Data, INT16 Data2)
 	}
 }
 
+void DACWrite16Signed(INT32 Chip, UINT16 Data)
+{
+#if defined FBA_DEBUG
+	if (!DebugSnd_DACInitted) bprintf(PRINT_ERROR, _T("DACWrite16 called without init\n"));
+	if (Chip > NumChips) bprintf(PRINT_ERROR, _T("DACWrite16 called with invalid chip number %x\n"), Chip);
+#endif
+
+	struct dac_info *ptr;
+
+	ptr = &dac_table[Chip];
+
+    INT16 Signed = Data - 0x8000;
+
+	Data = (INT32)(Signed * ptr->nVolume);
+
+	if (Data != ptr->Output) {
+		UpdateStream(Chip, ptr->pSyncCallback());
+		ptr->Output = Data;
+	}
+}
+
 void DACSignedWrite(INT32 Chip, UINT8 Data)
 {
 #if defined FBA_DEBUG
@@ -289,7 +342,10 @@ void DACReset()
 		ptr->nCurrentPosition = 0;
 		ptr->Output = 0;
 		ptr->Output2 = 0;
-	}
+    }
+
+    dac_lastin_r = dac_lastout_r = 0;
+	dac_lastin_l = dac_lastout_l = 0;
 }
 
 void DACExit()
@@ -313,7 +369,9 @@ void DACExit()
 	nDACCPUMHZ = 0;
 
 	NumChips = 0;
-
+
+    dac_dcblock = 0;
+
 	DebugSnd_DACInitted = 0;
 
 	BurnFree (lBuffer);

src/burn/snd/dac.h

@@ -1,12 +1,14 @@
 void DACUpdate(INT16* Buffer, INT32 Length);
 void DACWrite(INT32 Chip, UINT8 Data);
 void DACWrite16(INT32 Chip, INT16 Data);
+void DACWrite16Signed(INT32 Chip, UINT16 Data);
 void DACWrite16Stereo(INT32 Chip, INT16 Data, INT16 Data2);
 void DACSignedWrite(INT32 Chip, UINT8 Data);
 void DACInit(INT32 Num, UINT32 Clock, INT32 bAdd, INT32 (*pSyncCB)());
 void DACInit(INT32 Num, UINT32 Clock, INT32 bAdd, INT32 (*pCPUCyclesCB)(), INT32 nCpuMHZ);
 void DACSetRoute(INT32 Chip, double nVolume, INT32 nRouteDir);
 void DACStereoMode(INT32 Chip);
+void DACDCBlock(INT32 enable);
 void DACReset();
 void DACExit();
 void DACScan(INT32 nAction, INT32 *pnMin);