In the forward prediction case, we have with the input signal as the most up to date sample.
Then some features or quantities are calculated from a section of the input signal.
You drive the circuit with a square wave input signal a shown.
Positive feedback builds up the input signal to very high levels.
Others can vary the actual intensity in response to the input signal.
In this case (differential input signal), they are equal and opposite.
An input signal may have state specific behavior, if needed.
This carrier wave is usually a much higher frequency than the input signal.
Error (control) the deviation of an input signal from a set value.
However, in this case the input signal is made up of audible frequencies.