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Learning Quartz Composer: A Hands-On Guide to Creating Motion Graphics with Quartz Composer by Surya Buchwald, Graham Robinson

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Chapter 8. MIDI Interfacing (Getting Sliders and Knobs Involved)

MIDI controllers have historically been used to control audio software and hardware. With Quartz Composer, you can now use keyboards, drum machines, and banks of sliders and knobs to control visual elements.

MIDI Notes

Midi keyboards send out information encoded as “MIDI Notes,” which hold information on which key was pressed or released, and the corresponding velocity. Some programs listen for “Note On” and “Note Off” messages, while others—Quartz Composer, most importantly—simply use a “Note On” message with a Velocity of 0 to express a “Note Off” message. Remember, also, that Quartz Composer normalizes inputs to the 0–1 range. MIDI Note velocities are expressed as values in the ...

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