From 288b6454eeeb0cbd813ad75a94a6efdc112d6be9 Mon Sep 17 00:00:00 2001
From: OBattler <oubattler@gmail.com>
Date: Tue, 23 Sep 2025 17:55:46 +0200
Subject: [PATCH] AdLib Gold: Correctly use separate pseudo-stereo X and Y for
 the two sources.

---
 src/include/86box/filters.h | 18 +++++++++---------
 src/sound/snd_adlibgold.c   |  6 +++---
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/src/include/86box/filters.h b/src/include/86box/filters.h
index d11e79512..3e20fa653 100644
--- a/src/include/86box/filters.h
+++ b/src/include/86box/filters.h
@@ -75,7 +75,7 @@ adgold_lowpass_iir(int c, int i, float NewSample)
 
 /* fc=56Hz */
 static inline float
-adgold_pseudo_stereo_iir(float NewSample)
+adgold_pseudo_stereo_iir(int i, float NewSample)
 {
     float ACoef[NCoef + 1] = {
         0.00001409030866231767,
@@ -89,23 +89,23 @@ adgold_pseudo_stereo_iir(float NewSample)
         0.98738361004063568000
     };
 
-    static float y[NCoef + 1]; /* output samples */
-    static float x[NCoef + 1]; /* input samples */
+    static float y[2][NCoef + 1]; /* output samples */
+    static float x[2][NCoef + 1]; /* input samples */
     int          n;
 
     /* shift the old samples */
     for (n = NCoef; n > 0; n--) {
-        x[n] = x[n - 1];
-        y[n] = y[n - 1];
+        x[i][n] = x[i][n - 1];
+        y[i][n] = y[i][n - 1];
     }
 
     /* Calculate the new output */
-    x[0] = NewSample;
-    y[0] = ACoef[0] * x[0];
+    x[i][0] = NewSample;
+    y[i][0] = ACoef[0] * x[i][0];
     for (n = 1; n <= NCoef; n++)
-        y[0] += ACoef[n] * x[n] - BCoef[n] * y[n];
+        y[i][0] += ACoef[n] * x[i][n] - BCoef[n] * y[i][n];
 
-    return y[0];
+    return y[i][0];
 }
 
 /* fc=3.2kHz - probably incorrect */
diff --git a/src/sound/snd_adlibgold.c b/src/sound/snd_adlibgold.c
index 360da3fec..3be304cd7 100644
--- a/src/sound/snd_adlibgold.c
+++ b/src/sound/snd_adlibgold.c
@@ -82,7 +82,7 @@ typedef struct adgold_t {
     int treble;
     int bass;
 
-    int16_t opl_buffer[SOUNDBUFLEN * 2];
+    int16_t opl_buffer[MUSICBUFLEN * 2];
     int16_t mma_buffer[2][SOUNDBUFLEN];
 
     int pos;
@@ -829,7 +829,7 @@ adgold_get_buffer(int32_t *buffer, int len, void *priv)
             /*Filter left channel, leave right channel unchanged*/
             /*Filter cutoff is largely a guess*/
             for (c = 0; c < len * 2; c += 2)
-                adgold_buffer[c] += adgold_pseudo_stereo_iir(adgold_buffer[c]);
+                adgold_buffer[c] += adgold_pseudo_stereo_iir(0, adgold_buffer[c]);
             break;
         case 0x18: /*Spatial stereo*/
             /*Quite probably wrong, I only have the diagram in the TDA8425 datasheet
@@ -944,7 +944,7 @@ adgold_get_music_buffer(int32_t *buffer, int len, void *priv)
             /*Filter left channel, leave right channel unchanged*/
             /*Filter cutoff is largely a guess*/
             for (c = 0; c < len * 2; c += 2)
-                adgold_buffer[c] += adgold_pseudo_stereo_iir(adgold_buffer[c]);
+                adgold_buffer[c] += adgold_pseudo_stereo_iir(1, adgold_buffer[c]);
             break;
         case 0x18: /*Spatial stereo*/
             /*Quite probably wrong, I only have the diagram in the TDA8425 datasheet