Polarity

Overview

The term "Polarity" as applied to audio is used to describe the relationship of the electrical audio waveform to the original acoustic waveform.

• The audio waveform is considered to have "correct polarity" if the positive voltage section of the waveform corresponds to the positive air pressure section of the acoustic waveform. This is also referred to as "non-inverted" polarity.
• It is possible for the polarity of the waveform to be "inverted" by audio circuitry or connections. In the case of balanced connections, this is intentional and transparent because the inverted signal of the balanced output is re-inverted at he balanced input. In other cases; it may not be intentional and may be caused by an inverting amplifier or wiring issues. The audibility of polarity inversion can vary greatly with program material and the listening environment.

History

In the early days of audio, it was widely held that signal polarity was "not important" because inverting the polarity had no obvious audible effect. As audio technology progressed, advances such as the elimination of transformers and the development of "DC" audio circuitry made the effects of incorrect signal polarity more apparent. As a result; correct signal polarity is more likely to be maintained throughout the recording process.

Basics

The effect of incorrect signal polarity is that the speaker cone will move away from the listener when the original acoustic wave had a positive pressure and towards the listener when the acoustic pressure was negative.

Signal polarity is sometimes referred to as "absolute phase;" but this can be confusing as the term phase is used to describe a relative time relationship or delay between two signals. If a symmetric periodic waveform such as a sine wave is shifted 180 degrees in phase, it will appear to have the opposite polarity. But it actually has the same polarity it had prior to the phase-shift; it is only because of the similarity of the positive and negative half-cycles that it appears similar to the same waveform with inverted polarity.

Complex waveforms typical of music audio are quite different in this respect, with very different positive and negative half-cycles, and in many cases the portion of the waveform that is positive or negative may be more or less than one-half of the cycle as a result. For more related information; see waveform.