Out of phase stereo
Out of Phase Stereo (abbreviation OOPS ) was a popular method for improving spatial sound, especially in the 1970s. One speaker of the speaker pair is connected with reverse polarity (not phase-shifted), also called ("Left minus right"), so that the speaker membranes move in opposite directions. One of the a / b wires of the loudspeaker line is connected as b / a reversed. In this way, sounds with typical comb filter characteristics are generated.
The Swedish pop group ABBA made use of the OOPS method in some of their recordings, in which some audio tracks were copied and recorded “out of phase” on another free audio track .
Sometimes the term “phase shift by 180 °” and “ phase shift = 180 °” is incorrectly referred to, although only a simple b / a reverse polarity of two sound-carrying symmetrical a / b conductors is meant. In the case of a pure sine wave or some other symmetrical and periodic function, the inverted signal looks exactly like the 180 ° phase shifted one, but a phase shift is always achieved by shifting along the time axis, while the polarity reversal corresponds to a reflection on the time axis.
The signal below is exactly the mirrored original signal from above, as it appears with a simple polarity reversal. The signal in the middle, phase-shifted by 180 ° on the time axis, is something completely different and is not meant here. This is why the term “OOPS = Out-Of-Phase-Stereo” is incorrect when it comes to polarity reversal .
In technical jargon one speaks incorrectly of the phase-reversed stereo signal or of an incorrect phase position of an audio signal if the two wires of one of the two stereo channels have simply been swapped.
See also
Reverse polarity , phase reversal and phase shift .
Web links
- Reverse polarity and phase shift are different terms (PDF; 62 kB)