XY stereo system

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XY stereo microphone with 90 ° axis angle

The XY Stereophonic sound is a stereo - microphone method for loudspeaker stereophony . It only works with level differences between the left and right channels and therefore belongs to level difference or intensity stereophony .

description

With XY stereophony, two directional single microphones are arranged vertically one above the other with the smallest possible membrane spacing. The level differences result from the directivity of the microphones turned outwards. Thus, there is only Inter Channel - level difference and no Interchannel- time difference ; ∆ t = 0 ms.

The directional characteristics of the two directional microphones used are: wide cardioid, cardioid, supercardioid or hypercardioid. Diffuse field equalized pressure microphones with omnidirectional characteristics are also suitable; Pressure accumulation effect and acoustic shadows lead to directional effects at high frequencies, even with the sphere.

Due to the negligible microphone distance and the directional characteristics, when the XY microphones are angled, level differences arise between the signals from the two microphones, depending on the direction of the sound angle of incidence . This determines the recording range of the stereo microphone system. The microphones thus act like acoustic panpots . In the past, this type of recording was preferred for broadcasting because of its compatibility with mono. It also leads to sound recording with the greatest localization sharpness ; see web links.

There is therefore pure intensity stereophony. A level difference between ∆ L = 16 and 20 dB leads to a hearing event direction of 100%, i.e. fully from the direction of a loudspeaker. Mean calculated value ∆ L = 18 dB. The level differences .DELTA.L generated between the loudspeaker signals should not be confused with the frequency-dependent level differences ILD (Interaural Level Difference) that result as ear signals at the ears of the listener .

For the theory of intensity stereophony, in particular the generation of the loudspeaker signals and also for the recording area of ​​this XY main microphone system, see the web link below: "Theory Basics of 'Intensity' Stereophony".

The intensity stereophony also includes polymicrofoning , which works with completely separate mono microphone signals and whose phantom sound sources are set via panpots in the desired direction of the audio event on the loudspeaker base. This is the usual recording technique in light music. This simple merging of mono sound sources into a stereo panorama is also known as stick stereophony .

Mathematically equated with the XY recording technique is the MS recording technique (MS = center-side), in which the S-signal (directional signal) is generated by a side-facing microphone with figure eight characteristics. A microphone (center signal) with any directional characteristic can be directed towards the front of the sound source. The smallest possible distance should be between the microphones - which ideally is zero.

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

The most important processing means for mono signals in the case of intensity stereophony is the panpot (the panorama plate), which enables the placement of any audio event direction for phantom sound sources on the stereo loudspeaker base. The intensity stereophony is said to have the best localization sharpness .

To determine the phase position or the polarity reversal between the stereo signals L and R, a phase indicator called a correlation meter or a goniometer is used in intensity stereophony .

MS stereophony also belongs to the intensity stereophony .

Recording area vs. Sound body area for X / Y main microphones

The sound body area is the angle at which the sound body with its breadth can be "seen" from a certain point (in front of the sound body).

Basically (also for other miking), the recording area of ​​the main microphone should correspond to the area of ​​the sound box (no more and no less) if the sound box is to be completely reproduced on the basis of the playback speakers.

The mistake is often made that the microphones for X / Y are put together at an angle of 90 ° (and are therefore also offered as a "set" by the industry) and are arranged at a greater distance in front of the sound box. The result is a “tight” reproduction that is concentrated in the middle with poorly separated phantom sound sources .

The recording range of the X / Y system with a 90 ° microphone angle is greater than 180 °! (it is actually 196 °). Thus the system would have to be in the sound body in order to meet the above requirements.

An angle of 120 ° (recording range 160 °), 130 ° (recording range 148 °) or 150 ° (recording range 128 °) is better. The microphones can even be set up offset in height (180 ° angle). This results in a recording range of 102 °. Even if such an arrangement seems unusual, it has proven itself in practice.

(The recording angles can be found in the generally accessible specialist literature (Görne, Sengpiel, Dickreiter et al.)).

By calculating with the known angle functions , the following distances for the system to the sound body result for the angular positions:

  • 120 ° = 1/10 of the sound body expansion
  • 130 ° = 1/6 of the sound body expansion
  • 150 ° = ¼ of the sound body expansion
  • 180 ° = ½ of the sound body expansion

(The values ​​have been rounded for practical purposes)

An angle of at least 120 ° is therefore preferable in order to be able to position the main microphone in front of the sound box.

literature

  • Thomas Görne: Sound engineering. 1st edition. Carl Hanser Verlag, 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 .
  • Michael Dickreiter, Volker Dittel, Wolfgang Hoeg, Martin Wöhr (eds.): Manual of the recording studio technology. 8th, revised and expanded edition. 2 volumes, Verlag Walter de Gruyter, Berlin / Boston 2014, ISBN 978-3-11-028978-7 .

See also

Web links

Individual evidence

  1. ↑ [1] (PDF; 117 kB)
  2. ↑ [2] (PDF; 61 kB)