This program demonstrates how to get Scratch to hold a note for as long as a key is depressed, stopping the sound when the key is released, and allowing multiple notes to be played simultaneously in a chord. These are common issues faced by students in the interdisciplinary computing+music Sound Thinking course that I teach with Prof..Gena Greher of our Music Dept. (and formerly with Prof. Alex Ruthmann, now at NYU). The important things to understand are that (a) every note to be played must be in its own sprite, (b) the sustaining is accomplished by "turning the note on" with a play block that specifies the maximum of 999 beats and "turning the note off" by using the (new in Scratch 2.0) "stop other scripts in this sprite" block, and (c) while you can play a chord with all the "play note" blocks in the same sprite and trigger them individually (either simultaneously or arpeggio style) with a "broadcast," you can't stop them individually unless they're in separate sprites.
