... system can be described at various levels of abstraction, from a pictorial description or a schematic drawing at the lowest level to a block diagram at the highest level. For the purposes of the ... acceptable audio level, is amplified in the stereo amplifier. The amplifier increases the power level to a point at which it can drive the loudspeakers. In mathematical terms, if the power level input ... the highest level. For the purposes of the present discussion, this higher -level abstraction is preferable. At this level, each functional subsystem is characterized by inputs, outputs, and...