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