Still interested in sound, I have been playing around with it in C using t&s history of ES, I plan to do something along these lines. Due to canceled orders/fake size, using market depth/level II as the data for the sound is flawed. Instead I plan to take the history of trades (which is what really counts anyways) and working from that. Similar to the made up story posted, orders hitting the ask are major chords and orders hitting the bid are minor chords. I will also compare current price to an average of the last 1 minute (I have considered different lengths, will have to play around with it if I code this) of trades weighted by size, the further price is above it the higher the chord, the further below it the lower the chord. That way you can actually hear market exhaustions, an exhaustion to the upside would sound like notes rising in major very quickly and then suddenly dropping to low minor chords. As far as including size in the equation, I think the best way to do it would be to make volume a functon of size. That way, if you have a bunch of small orders go off at the bid mixed with large orders going off at the ask you would hear a few quiet minor chords in the background and the occasional loud major chord. Any suggestions? I don't really plan on trading using this but just thought that it would be extremely cool to listen to.