put the volume script on the show notes page stub, rather than in the shortcode. Volume will ONLY get set on shownotes pages

layouts/shortcodes/audio.html

@@ -2,10 +2,4 @@
     <audio id="audio_player" style="width:80%" onloadeddata="set_volume()" controls>
         <source src="{{ index .Params 0 }}" type="audio/mpeg">
     </audio>
-    <script>
-        let audio = document.getElementById("audio_player");
-        function set_volume(){
-            audio.volume = 0.4;
-        }
-    </script>
 </div>

layouts/shownote/single.html

@@ -13,6 +13,13 @@
     </span>
     {{ end }}
     {{ .Content }}
+    <script>
+        let audio = document.getElementById("audio_player");
+
+        function set_volume(){
+            audio.volume = 0.4;
+        }
+    </script>
 </div>
 
 {{ partial "footer.html" . }}