Equivalence stereophony

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Equivalence stereophony or mixed stereophony is a recording method used for miking for loudspeaker stereophony . In this method, the same direction and frequency are neutral Inter Channel - level differences Δ L and simultaneously the Interchannel- time differences Δ t in a main microphone system used. The word equivalence here comes from the joint adding effect of the time difference and level difference to the migration of phantom sound sources from the loudspeaker center. The generated sound pressure differences (level differences) follow the distance lawwith 1 / r .

Microphones / miking

What all these microphone systems have in common is that usually two small-diaphragm condenser microphones with cardioid characteristics are used in one plane. Depending on the system, different angles are used between the microphones ( axis angle ) and distances between the microphones ( microphone base ). The recording area = recording angle is usually smaller than the axis angle (exception: EBS miking: both angles are the same) and results from the arrangement.

The angular position enables the direction of the phantom sound sources to be localized through level differences on the stereo basis of the loudspeakers; Depending on the type of miking, the focus is on the localization sharpness or the spatial perception of a sound event.

For equivalence stereophony, directional characteristics other than the cardioid are used in individual cases .

Well-known miking are:

  • ORTF (Office de Radiodiffusion Télévision Française, French radio), axis angle 110 °, recording angle 96 °, microphone base 17 cm, level proportion 60.6%, transit time proportion 39.4%
  • NOS (Nederlandse Omroep Stichting, Dutch Broadcasting), axis angle 90 °, recording angle 81 °, microphone base 30 cm, level proportion 42.3%. Term share 57.6%
  • EBS ( Eberhard Sengpiel ) axis angle 90 °, recording angle 90 °, microphone base 25 cm, level component 46.8%, runtime component 53.1%. Special feature: mounting angle = axis angle
  • RAI (Radio Italia, Italienischer Rundfunk), axis angle 100 °, recording angle 93 °, microphone base 21 cm, level component 53.4%, transit time component 46.6%
  • DIN (German Industrial Standards Committee), axis angle 90 °, recording angle 101 °, microphone base 20 cm, level component 52.6%, transit time component 47.3%
  • LTE (level / time equality, Markus Brückner), axis angle 90 °, recording angle 96 °, microphone base 22 cm, level component 50%, transit time component 50%. Special feature: level component = transit time component

The EBS miking has some remarkable properties in practice: The runtime component is comparatively high; the recording is given a good spatiality. The recording angle is the same as the microphone angle , which enables good visual control of the recording angle ("bearing via the microphones"). With a recording angle of 90 °, the distance between the microphone system is half the extent of the sound body (proof: angle functions ) if the sound body is the stereo base should fill when playing through speakers.

A special case of equivalence stereophony is the combination of transit time stereophony and intensity stereophony with a microphone at the same place (Kraglund arrangement). In the middle between two microphones (with omnidirectional characteristics, distance approx. 30 cm), which enable a time-differentiated recording, there are two microphones (with cardioid characteristics). They are set up in a strict "x / y arrangement" (for intensity stereophony). The four microphones are attached to a common "rail". The two pairs of stereo signals are fed either to a four-channel recording device or to a mixer . The transit time signals and the intensity signals can be mixed here in any ratio (which is not possible with arrangements such as ORTF, NOS etc.). This form of miking has proven itself in situations where the acoustic conditions of the recording location are unknown or confusing and the “classic” miking does not lead to the desired result. The optimization takes place less during the recording, more so in the post-processing.

differences

The word loudspeaker stereophony is used to distinguish it from headphone stereophony, which includes an artificial head microphone arrangement for recording and headphones for playback. The previously unclear terms of room-related and head-related stereophony should be avoided because ultimately the head with the ears is always needed for listening, ie it is "head-related".

For the theory of equivalence stereophony, in particular the generation of the loudspeaker signals and also the recording area of this main microphone system, see the web links of this article. The use of these signal differences is called equivalence .

A sound recording with a main microphone system is often supplemented by support microphones and room microphones.

literature

  • Thomas Görne: Sound engineering. 1st edition, Carl Hanser, Leipzig 2006, ISBN 3-446-40198-9
  • Thomas Görne: Microphones in theory and practice. 8th edition, Elektor-Verlag, Aachen 2007, ISBN 978-3-89576-189-8

See also

Web links