Sound instrument development

I need some competent suggestions on where to start with developing an audio tool. I have been involved in graphic programming for several years and thought it would be a refreshing experience to expand my knowledge in a completely different direction. Where do you see a good starting point for a beginner like me? For starters, some lines of code producing cacophonic sounds will make me happy. What audio API would you recommend when using cross-platform support? What should I consider as a whole?

I most likely skipped to give you important information so that my intentions are clear, so just ask!

Thanks in advance!:)