I am working on a recorder app and need to generate audio spectrum for my files. I need to get amplitude list from audio file so that I can draw audio wave with Canvas by my own.

I have read the fantastic answer by llogan. However, I don’t know how to set the time interval manually. By the way, when I try to run the command, I got a list full of negetive numbers: command-running-image. Hope someone can explain it.