diff --git a/generator/ruby/soundfont_builder.rb b/generator/ruby/soundfont_builder.rb
index 9d31bc0a..9e7f91cd 100755
--- a/generator/ruby/soundfont_builder.rb
+++ b/generator/ruby/soundfont_builder.rb
@@ -34,9 +34,11 @@
 # This script will generate MIDI.js-compatible instrument JS files for
 # all instruments in the below array. Add or remove as necessary.
 INSTRUMENTS = [
+  -1,   # Percussion (channel 10)
   0     # Acoustic Grand Piano
 ];
 # INSTRUMENTS = [
+#   -1,    # Percussion (channel 10)
 #   0,     # Acoustic Grand Piano
 #   24,    # Acoustic Guitar (nylon)
 #   25,    # Acoustic Guitar (steel)
@@ -64,7 +66,11 @@
 
 # Display instrument names.
 INSTRUMENTS.each do |i|
-  puts "    #{i}: " + MIDI::GM_PATCH_NAMES[i]
+  if i == -1
+    puts "    percussion (MIDI channel 10)"
+  else
+    puts "    #{i}: " + MIDI::GM_PATCH_NAMES[i]
+  end
 end
 
 puts
@@ -137,11 +143,16 @@ def generate_midi(program, note_value, file)
   include MIDI
   seq = Sequence.new()
   track = Track.new(seq)
+  channel = 0
+  if program == -1
+    channel = 9
+    program = 0
+  end
 
   seq.tracks << track
-  track.events << ProgramChange.new(0, Integer(program))
-  track.events << NoteOn.new(0, note_value, VELOCITY, 0) # channel, note, velocity, delta
-  track.events << NoteOff.new(0, note_value, VELOCITY, DURATION)
+  track.events << ProgramChange.new(channel, Integer(program))
+  track.events << NoteOn.new(channel, note_value, VELOCITY, 0) # channel, note, velocity, delta
+  track.events << NoteOff.new(channel, note_value, VELOCITY, DURATION)
 
   File.open(file, 'wb') { | file | seq.write(file) }
 end
@@ -183,7 +194,11 @@ def base64js(note, file, type)
 
 def generate_audio(program)
   include MIDI
-  instrument = GM_PATCH_NAMES[program]
+  if program == -1
+    instrument = "percussion"
+  else
+    instrument = GM_PATCH_NAMES[program]
+  end
   instrument_key = instrument.downcase.gsub(/[^a-z0-9 ]/, "").gsub(/\s+/, "_")
 
   puts "Generating audio for: " + instrument + "(#{instrument_key})"
diff --git a/js/midi/gm.js b/js/midi/gm.js
index 2e1278ca..dc17d5a4 100644
--- a/js/midi/gm.js
+++ b/js/midi/gm.js
@@ -49,7 +49,8 @@
 		'Synth Effects': ['97 FX 1 (rain)', '98 FX 2 (soundtrack)', '99 FX 3 (crystal)', '100 FX 4 (atmosphere)', '101 FX 5 (brightness)', '102 FX 6 (goblins)', '103 FX 7 (echoes)', '104 FX 8 (sci-fi)'],
 		'Ethnic': ['105 Sitar', '106 Banjo', '107 Shamisen', '108 Koto', '109 Kalimba', '110 Bagpipe', '111 Fiddle', '112 Shanai'],
 		'Percussive': ['113 Tinkle Bell', '114 Agogo', '115 Steel Drums', '116 Woodblock', '117 Taiko Drum', '118 Melodic Tom', '119 Synth Drum'],
-		'Sound effects': ['120 Reverse Cymbal', '121 Guitar Fret Noise', '122 Breath Noise', '123 Seashore', '124 Bird Tweet', '125 Telephone Ring', '126 Helicopter', '127 Applause', '128 Gunshot']
+		'Sound effects': ['120 Reverse Cymbal', '121 Guitar Fret Noise', '122 Breath Noise', '123 Seashore', '124 Bird Tweet', '125 Telephone Ring', '126 Helicopter', '127 Applause', '128 Gunshot'],
+		'Percussion': ['0 Percussion'] // not really GM but convenient hack
 	});
 
 	/* get/setInstrument
@@ -138,6 +139,7 @@
 				solo: false
 			};
 		}
+		channels[9].instrument = -1; // channel 10 is percussion
 		return channels;
 	})();
 
diff --git a/js/midi/plugin.webaudio.js b/js/midi/plugin.webaudio.js
index 15a6f0a7..00352f8b 100644
--- a/js/midi/plugin.webaudio.js
+++ b/js/midi/plugin.webaudio.js
@@ -235,7 +235,7 @@
 			var notes = root.keyToNote;
 			for (var key in notes) urls.push(key);
 			///
-			var waitForEnd = function(instrument) {
+			var waitForEnd = function() {
 				for (var key in bufferPending) { // has pending items
 					if (bufferPending[key]) return;
 				}
@@ -259,7 +259,7 @@
 							var percent = index / 87;
 // 							console.log(MIDI.GM.byId[instrumentId], 'processing: ', percent);
 							soundfont.isLoaded = true;
-							waitForEnd(instrument);
+							waitForEnd();
 						}
 					}, function(err) {
 		// 				console.log(err);