Phantom source

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Phantom sound source , a term from the stereophony of audio technology , is a virtual sound source that is perceived by the listener between the actual two radiating sound sources, the loudspeakers .


The virtual sound transmitter appears at the intersection of the vertical line with the loudspeaker base (compare base width ) for a listener located on this same center line if both stereo loudspeakers emit the same signal (same in frequency composition, level and phase) in exactly the same way. A characteristic feature of the phantom sound source is that its perception is based on the localization stimuli of several real sound sources - in the simplest case, a centrally perceived sound source that comes from the two real sound sources "loudspeakers" in stereo playback. The term should not be confused with a "virtual sound source" that can be found in wave field synthesis , artificial head stereophony and the "mirror sound source" . The latter are parasitic multiple images due to sound reflections.

Phantom sound sources have an audio event direction or a listening location that only exists in the mind of the listener. If the location of the auditory event occurs as a result of at least two localization stimuli, the fictitious sound source is a phantom sound source. With loudspeaker stereophony , we are dealing with phantom sound sources, the perceived expansion of which must differ considerably from real sound sources depending on their properties. It can be illustrated that in natural hearing, through the geometry of our head , we naturally generate interaural level differences ( ILD ) and interaural transit time differences ( ITD ) ourselves, while phantom sound sources use level differences Δ L and / or transit time differences Δ t between the two speakers as Real sound sources are generated. The use of these signal differences is called equivalence .

Mixing console technology

In mixing consoles, so-called panpots (panorama potentiometers, panorama controls, panorama controls ) are used in intensity stereophony to distribute single-channel signals between left and right in any direction as phantom sound sources, with level differences being generated by voltage dividers. Mixer manufacturers only take the intensity stereophony as given, as it is mainly used by radio because of its perfect mono compatibility and pop music because of the "robust" and simple mixing technology and the easy generation of stereo directions.

Localization of the sound sources

Here, phantom sound sources can turn out to be problematic due to the cumulative localization, prone to interference in their localization and discolored in their sound. Compared to natural sound sources, they have a less precise listening location and seem to be less present, because both ears are outside the center even with a central listening position (sweet spot) and can thus be reached by the loudspeaker signals one after the other. In this way, frequency-dependent cancellations and amplifications can be measured in the same way on each ear, i.e. a typical sound color corresponding to a comb filter . In fact, this effect cannot or can hardly be observed, as the hearing corrects the color itself without being noticed. The elevation ( the elevation ) of the phantom sound sources on the line connecting the loudspeakers results from the contradiction that while the auditory receives identical signals in a real center sound source, but in fact this does not arrive from the front, but by half the side. The associated sound color falsification must appear illogical to the ear from its experience. It reacts with the apparent elevation of the phantom sound source - compare also Blauert's bands . A narrow-band level increase in the range of 8 kHz in a center signal leads to an elevation of the localization of this phantom sound source beyond the horizontal loudspeaker level.


It can be assumed that the reproduction is of higher quality the sharper and more precise the phantom sound sources are. This is a reliable way of subjectively assessing the image quality. On the other hand, many listeners appreciate a high ASW (Apparent Source Width), as it corresponds more to the perception in a concert hall. Sound sources are perceived diffuse and spatially extended. Certain properties of a loudspeaker (wide radiation pattern) and the room (strong initial reflections from the side) can cause an increase in the ASW. However, this reduces the localization sharpness of phantom sound sources.

On the other hand, it is more difficult to judge a correct reproduction of the spatiality (width, depth, ASW, LEV (Listener Envelopment)). There are no fixed indications for the "correctness" of the reproduction. This is rather the other way around defined by suitable listening conditions: "More natural", "real", "authentic" or "original" spatial impression are not suitable descriptive features of stereo reproduction, as it is subject to fundamental restrictions.


  • Michael Dickreiter, Volker Dittel, Wolfgang Hoeg, Martin Wöhr (eds.): Handbuch der Tonstudiotechnik , 8th, revised and expanded edition, 2 volumes, publisher: Walter de Gruyter, Berlin / Boston, 2014, ISBN 978-3-11- 028978-7 or e- ISBN 978-3-11-031650-6
  • Peter M. Pfleiderer: HIFI in a nutshell, playback technology for unadulterated hearing. 1st edition, Richard Pflaum Verlag, Munich, 1990, ISBN 3-7905-0571-4
  • Hubert Henle: The recording studio manual. 5th edition, GC Carstensen Verlag, Munich, 2001, ISBN 3-910098-19-3

See also

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