Animated sound waveform
APL (61)

{∇n⊣⎕DL.1⊣⎕SM←1 1,⍨⊂' '⍪⊖⍉↑⍴∘'▇'¨,0,⍪n←24⌊0⌈⍵+3-?5/⍨⍴⍵}?24/40


It starts with random-sized bars, and changes the height of each of the bars by a random number between -2 and 2 each frame.

Screenshot: