diff --git a/ooktools/commands/converstions.py b/ooktools/commands/converstions.py
index 1fa4e0d..fbf0634 100644
--- a/ooktools/commands/converstions.py
+++ b/ooktools/commands/converstions.py
@@ -72,6 +72,6 @@ def clean_pwm_wave(source, destination):
         frames.append(struct.pack('h', value))
 
     click.secho('Writing output to file: {}'.format(destination))
-    output_wave.writeframes(''.join(frames))
+    output_wave.writeframes(b''.join(frames))
 
     return