The IDEAL FREQUENCY RESPONSE of an audio amplifier is equal gain from 15 Hz to 20 kHz
with very low gain outside of those limits.
A PHASE SPLITTER provides two output signals that are equal in amplitude but different in phase
from a single input signal. Phase splitters are often used to provide input signals to a push-pull amplifier.
A PUSH-PULL AMPLIFIER uses two transistors whose output signals are added together to
provide a larger gain (usually a power gain) than a single transistor could provide. Push-pull amplifiers
can be operated class A, class AB or class B.