diff --git a/scripts/led-matrix-viz.py b/scripts/led-matrix-viz.py
index d054188..89ef3e6 100755
--- a/scripts/led-matrix-viz.py
+++ b/scripts/led-matrix-viz.py
@@ -131,6 +131,7 @@ def main():
                                 changed = True
                         if changed:
                             events_processed += 1
+                            print(f"[viz] note {note} {'on' if vel > 0 else 'off'} active={len(active_notes)}", flush=True)
                             params = render(active_notes)
                             if params != last_sent_params:
                                 msg_id = (msg_id + 1) % 65535
@@ -143,8 +144,10 @@ def main():
             if ok:
                 pending_bytes = None
                 frames_sent += 1
+                print(f"[viz] sent frame #{msg_id}", flush=True)
             else:
                 frames_dropped += 1
+                print(f"[viz] drop frame #{msg_id}", flush=True)
 
         # Background refresh: resend last params to recover from router drops
         if refresh_due: