I am making a simple metronome where it plays a tick sound every few milliseconds depending on the bpm and plays the sound using the winsound module. I use tkinter because there will be a gui component later but for now the metronome code is working, it plays the sound at a constant rate, but even though I set the after loop to play the sound every few milliseconds, it waits longer and the beat is slower than it should be. Is it a problem with the code or a problem with the way I calculate the time? Thanks. Here is my code. from Tkinter import * import winsound,time,threading root=Tk() c=Canvas(root) c.pack() class metronome(): def __init__(self,root,canvas,tempo=100): self.root=root self.root.bind("<1>",self.stop) self.c=canvas self.thread=threading.Thread(target=self.play) self.thread.daemon=True self.pause=False self.tempo=tempo/60.0 self.tempo=1.0/self.tempo self.tempo*=1000 def play(self): winsound.PlaySound("tick.wav",winsound.SND_FILENAME) self.sound=self.c.after(int(self.tempo),self.play) def stop(self,e): self.c.after_cancel(self.sound) beat=metronome(root,c,120) beat.thread.start() root.mainloop()