ABSTRACT
In general acoustic terms, amplitude describes changes in air pressure compared to the normal atmospheric pressure. A microphone converts changes in air pressure to voltages. An A/D converter converts these voltages into discrete numbers. Changes in air pressure happen above and below the normal atmospheric pressure (the zero reference), resulting in sound amplitude that is bipolar – it has both positive and negative magnitudes. The voltages and numbers used to describe audio signals are also bipolar. An audio system has an equal positive and negative capacity. Professional audio gear, for example, uses −1.23 to +1.23 volts; an audio sequencer uses the −1 to +1 rational range.
