I'm looking for a software that works with Arduino that uses something like Audacity to help sync it to the music. Its for a Firework controller firing 150 relays. Any Idea? Or am I going to have to really write ALL that code?

What about MAX/MSP plug-in for Abelton music software? i think this will allow all the interaction you could need between a music platform and the arduino it's all ready set up for it and there is loads of people all ready doing it so coding it should be a lot easier

Awesome! exactly what im looking for a think. But do I really have to pay $300 for Ableton? And which version is best? and what all else do I need for the 2 to talk to each other?

I'm Using Arduino Mega with SN74HC595 To control 150 relays, will Ableton be able to understand all that?

Is there a cheaper version of ableton?

Abelton should have no problem with the relays. Yes it is a bit expensive I think you get a free version with some sound cards. So if you haven't got one already thats an option. I think a cut down version (which will do fine as far as i know) comes free with these sound card. Check but it definitely come with one of them. It's a much cheaper way to get it