First, we will allow the pitch of the tone to be defined as a parameter in the score. Score parameters can be represented by orchestra variables which take on their different values on successive notes. Next, suppose we want to shape the amplitude of our tone with a linear rise from 0 to 10000. It is really a variable whose purpose is to control the amplitude of the audio oscillator. Although audio output requires fine resolution in time for good fidelity, a controlling signal often does not need that much resolution.
Control signals are identical to audio signals, differing only in their resolution in time.
A control signal changes its value less often than an audio signal, and is thus faster to generate. This would likely be indistinguishable in sound from the first version, but would run a little faster. In general, instruments take constants and parameter values, and use calculations and signal processing to move first towards the generation of control signals, then finally audio signals. Remembering this flow will help you write efficient instruments with faster execution times. We are now ready to create our first orchestra file.