From 70f512003e590ce382807715b1cf42d6bc413b63 Mon Sep 17 00:00:00 2001
From: tildearrow <me@tildearrow.org>
Date: Tue, 16 Sep 2025 03:05:27 -0500
Subject: [PATCH] OPN: fix wrong getGain in ExtCh

---
 src/engine/platform/fmshared_OPN.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/engine/platform/fmshared_OPN.h b/src/engine/platform/fmshared_OPN.h
index cd1bef62f..2b301dd6a 100644
--- a/src/engine/platform/fmshared_OPN.h
+++ b/src/engine/platform/fmshared_OPN.h
@@ -214,6 +214,13 @@ class DivPlatformOPN: public DivPlatformFMBase {
       return DivPlatformFMBase::mapVelocity(ch,vel);
     }
     virtual float getGain(int ch, int vol) {
+      if (extSys) {
+        if (ch>=extChanOffs+4) {
+          ch-=4;
+        } else if (ch>=extChanOffs) {
+          ch=extChanOffs;
+        }
+      }
       if (vol==0) return 0;
       if (ch==csmChan) return 1;
       if (ch==adpcmBChanOffs) return (float)vol/255.0;