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Fix (rarely audible) click bug in BLEP synthesis

Fixes random clicks in specific pitch sweep tests I made. These clicks shouldn't have been present. This bug was introduced in v1.34.

--- a/src/pt2_audio.c

+++ b/src/pt2_audio.c

@@ -284,12 +284,13 @@

 		v->dOldVoiceDeltaMul = 1.0 / v->dOldVoiceDelta;

 	}

+	// to be read on next sampling step

 	v->AUD_PER_delta = v->dOldVoiceDelta;

-	

+	v->AUD_PER_deltamul = v->dOldVoiceDeltaMul;

+

 	// set BLEP stuff

-	v->dDeltaMul = v->dOldVoiceDeltaMul;

-	if (v->dLastDelta == 0.0)

-		v->dLastDelta = v->AUD_PER_delta;

+	if (v->dLastDelta    == 0.0) v->dLastDelta    = v->AUD_PER_delta;

+	if (v->dLastDeltaMul == 0.0) v->dLastDeltaMul = v->AUD_PER_deltamul;

 }

 void paulaSetVolume(int32_t ch, uint16_t vol)

@@ -385,8 +386,10 @@

 	v->sampleCounter--;

 	// set BLEP stuff

+	v->dDeltaMul = v->AUD_PER_deltamul;

 	v->dLastPhase = 0.0;

 	v->dLastDelta = v->dDelta;

+	v->dLastDeltaMul = v->dDeltaMul;

 	v->dBlepOffset = 0.0;

 	v->dPhase = 0.0;

@@ -473,8 +476,15 @@

 			{

 				v->dPhase -= 1.0;

+				// set BLEP stuff

+				v->dLastPhase = v->dPhase;

+				v->dLastDelta = v->dDelta;

+				v->dLastDeltaMul = v->dDeltaMul;

+				v->dBlepOffset = v->dLastPhase * v->dLastDeltaMul;

+

 				// Paula only updates period (delta) during period refetching (this stage)

 				v->dDelta = v->AUD_PER_delta;

+				v->dDeltaMul = v->AUD_PER_deltamul;

 				if (v->sampleCounter == 0)

 				{

@@ -495,7 +505,7 @@

 				/* Pre-compute current sample point.

 				** Output volume is only read from AUDxVOL at this stage,

 				** and we don't emulate volume PWM anyway, so we can

-				** pre-multiply by volume at this point.

+				** pre-multiply by volume here.

 				*/

 				v->dSample = v->AUD_DAT[0] * v->AUD_VOL; // -128..127 * 0.0 .. 1.0

@@ -502,11 +512,6 @@

 				// progress AUD_DAT buffer

 				v->AUD_DAT[0] = v->AUD_DAT[1];

 				v->sampleCounter--;

-

-				// setup BLEP stuff

-				v->dBlepOffset = v->dPhase * v->dDeltaMul;

-				v->dLastPhase = v->dPhase;

-				v->dLastDelta = v->dDelta;

 			}

 		}

 	}

--- a/src/pt2_audio.h

+++ b/src/pt2_audio.h

@@ -37,13 +37,13 @@

 	// registers modified by Paula functions

 	const int8_t* AUD_LC; // location

 	uint16_t AUD_LEN; // length (in words)

-	double AUD_PER_delta; // delta

+	double AUD_PER_delta, AUD_PER_deltamul; // delta

 	double AUD_VOL; // volume

 	double dDelta, dPhase;

 	// for BLEP synthesis

-	double dLastDelta, dLastPhase, dBlepOffset, dDeltaMul;

+	double dLastDelta, dLastPhase, dLastDeltaMul, dBlepOffset, dDeltaMul;

 	// period cache

 	int32_t oldPeriod;

--- a/src/pt2_header.h

+++ b/src/pt2_header.h

@@ -14,7 +14,7 @@

 #include "pt2_unicode.h"

 #include "pt2_palette.h"

-#define PROG_VER_STR "1.41"

+#define PROG_VER_STR "1.42"

 #ifdef _WIN32

 #define DIR_DELIMITER '\\'