clear [midi] plugin audio output buffers before running plugin.

some samplers don't zero the output buffers if they're not configured
or no samples are loaded.

diff --git a/libs/ardour/plugin_insert.cc b/libs/ardour/plugin_insert.cc
index 443e1b565e60424540f01e618b374d648de92990..a58a25fb9fb67409096a1876bc6f6be6bc49c411 100644 (file)
--- a/libs/ardour/plugin_insert.cc
+++ b/libs/ardour/plugin_insert.cc
@@ -635,10 +635,18 @@ PluginInsert::connect_and_run (BufferSet& bufs, pframes_t nframes, framecnt_t of
                        for (uint32_t out = 0; out < bufs.count().get (*t); ++out) {
                                bool valid;
                                uint32_t in_idx = thru_map.get (*t, out, &valid);
+                               uint32_t m = out + natural_input_streams ().get (*t);
                                if (valid) {
-                                       uint32_t m = out + natural_input_streams ().get (*t);
                                        _delaybuffers.delay (*t, out, inplace_bufs.get (*t, m), bufs.get (*t, in_idx), nframes, offset, offset);
                                        used_outputs.set (*t, out, 1); // mark as used
+                               } else {
+                                       used_outputs.get (*t, out, &valid);
+                                       if (valid) {
+                                               /* the plugin is expected to write here, but may not :(
+                                                * (e.g. drumgizmo w/o kit loaded)
+                                                */
+                                               inplace_bufs.get (*t, m).silence (nframes);
+                                       }
                                }
                        }
                }