Avisu is a very quick, low latency Audio VISUalizer app for the iPad and iPhone. It allows you to see the music you are hearing via several different spectrum analyzer styles and claims to have very low latency. The four unique scalable visualizer styles in come in five colors, allowing you to envision either your iPod/iTunes tracks or sound picked up by the microphone input.
The raw data of your iPod/iTunes tracks is processed internally for precision. Audio from other apps continues to play while visualizing the microphone input, so you can visualize your favorite internet radio or other sources. The real time scale function provides the ability to set-up the visualizer to your own specifications.