control signal

1/4 of a sine wave as a control shape

The cycle~ object uses a lookup table of 512 values that make the shape of a single cycle of a cosine wave, and it reads through those repeatedly at whatever rate is specified in its left (frequency) inlet. You can also set the cycle~ to 0 Hz (its default frequency) and select a point in the cosine waveform with a value (either a signal or a float) from 0 to 1 in the right (phase offset) inlet.

Simple amplitude control

When you're changing the amplitude of a sound, if the amplitude is changed very suddenly and significantly, it may create a sudden discontinuity in the waveform which will be heard as a high-frequency click. (That phenomenon is demonstrated in the example "Click resulting from amplitude change".) To avoid that problem, it's necessary to interpolate sample-by-sample from the old amplitude value to the new value, over some small period of time, to create a slightly more gentle fade to the new amplitude factor.