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[Core/Sound] improved PSG accuracy (fixes high-frequency aliasing noises in Captain Silver, Kenseiden, Phantasy Star & many other SMS games, thanks to Enik for the help)

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EkeEke 2016-12-18 22:38:50 +01:00
parent 8feabd5eaf
commit eedbfecac9
1 changed files with 22 additions and 28 deletions
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50
core/sound/sn76489.c
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@ -38,6 +38,12 @@
- Re-added stereo GG support
- Re-added configurable Feedback and Shift Register Width
- Rewrote core with various optimizations
04/11/16 Eke-Eke (Genesis Plus GX)
- improved resampling quality (removes aliasing noise when using high frequency tones)
- removed cut-off value (improves emulation accuracy of highest frequency tones)
- modified channels output to 0/1 like real chip instead of -1/+1 (fixes PCM voices when cut-off value is removed)
*/
#include "shared.h"
@ -47,10 +53,6 @@
/* Initial state of shift register */
#define NoiseInitialState 0x8000
/* Value below which PSG does not output */
/*#define PSG_CUTOFF 0x6*/
#define PSG_CUTOFF 0x1
/* original Texas Instruments TMS SN76489AN (rev. A) used in SG-1000, SC-3000H & SF-7000 computers */
#define FB_DISCRETE 0x0006
#define SRW_DISCRETE 15
@ -172,7 +174,7 @@ INLINE void UpdateToneAmplitude(int i, int time)
if (delta != 0)
{
SN76489.ChanOut[i][0] += delta;
blip_add_delta_fast(snd.blips[0][0], time, delta);
blip_add_delta(snd.blips[0][0], time, delta);
}
/* right output */
@ -180,7 +182,7 @@ INLINE void UpdateToneAmplitude(int i, int time)
if (delta != 0)
{
SN76489.ChanOut[i][1] += delta;
blip_add_delta_fast(snd.blips[0][1], time, delta);
blip_add_delta(snd.blips[0][1], time, delta);
}
}
@ -194,7 +196,7 @@ INLINE void UpdateNoiseAmplitude(int time)
if (delta != 0)
{
SN76489.ChanOut[3][0] += delta;
blip_add_delta_fast(snd.blips[0][0], time, delta);
blip_add_delta(snd.blips[0][0], time, delta);
}
/* right output */
@ -202,7 +204,7 @@ INLINE void UpdateNoiseAmplitude(int time)
if (delta != 0)
{
SN76489.ChanOut[3][1] += delta;
blip_add_delta_fast(snd.blips[0][1], time, delta);
blip_add_delta(snd.blips[0][1], time, delta);
}
}
@ -220,13 +222,8 @@ static void RunTone(int i, int clocks)
/* Process any transitions that occur within clocks we're running */
while (time < clocks)
{
if (SN76489.Registers[i*2]>PSG_CUTOFF) {
/* Flip the flip-flop */
SN76489.ToneFreqPos[i] = -SN76489.ToneFreqPos[i];
} else {
/* stuck value */
SN76489.ToneFreqPos[i] = 1;
}
/* Flip the flip-flop */
SN76489.ToneFreqPos[i] ^= 1;
UpdateToneAmplitude(i, time);
/* Advance to time of next transition */
@ -260,8 +257,8 @@ static void RunNoise(int clocks)
while (time < clocks)
{
/* Flip the flip-flop */
SN76489.ToneFreqPos[3] = -SN76489.ToneFreqPos[3];
if (SN76489.ToneFreqPos[3] == 1)
SN76489.ToneFreqPos[3] ^= 1;
if (SN76489.ToneFreqPos[3])
{
/* On the positive edge of the square wave (only once per cycle) */
int Feedback = SN76489.NoiseShiftRegister;
@ -323,12 +320,9 @@ void SN76489_Config(unsigned int clocks, int preAmp, int boostNoise, int stereo)
SN76489.PreAmp[i][0] = preAmp * ((stereo >> (i + 4)) & 1);
SN76489.PreAmp[i][1] = preAmp * ((stereo >> (i + 0)) & 1);
/* noise channel boost */
if (i == 3)
{
SN76489.PreAmp[3][0] = SN76489.PreAmp[3][0] << boostNoise;
SN76489.PreAmp[3][1] = SN76489.PreAmp[3][1] << boostNoise;
}
/* noise channel boost (applied to all channels) */
SN76489.PreAmp[i][0] = SN76489.PreAmp[i][0] << boostNoise;
SN76489.PreAmp[i][1] = SN76489.PreAmp[i][1] << boostNoise;
/* update stereo channel amplitude */
SN76489.Channel[i][0]= (PSGVolumeValues[SN76489.Registers[i*2 + 1]] * SN76489.PreAmp[i][0]) / 100;
@ -352,11 +346,11 @@ void SN76489_Update(unsigned int clocks)
/* Adjust internal M-cycle counter for next frame */
SN76489.clocks -= clocks;
/* Adjust channel time counters for new frame */
for (i=0; i<4; ++i)
{
SN76489.ToneFreqVals[i] -= clocks;
}
/* Adjust channel time counters for new frame */
for (i=0; i<4; ++i)
{
SN76489.ToneFreqVals[i] -= clocks;
}
}
void SN76489_Write(unsigned int clocks, unsigned int data)