Stereophonic sound#X-Y technique: intensity stereophony

Intensity stereophony, also called Pegeldifferenzstereofonie, a method of the loudspeaker stereophony to achieve a stereo effect for the sense of hearing. The direction of localization of a sound source included in the sound field of the two stereo speakers arises by means of level differences.

General

Another name for intensity stereophony is Pegeldifferenzstereofonie. For the right-left differences of sound intensities corresponding differences in sound pressure level, which act on the human ears. Other methods for generating a stereo field work as Äquivalenzstereofonie addition to level differences with differences in transit time or as Laufzeitstereofonie mainly with maturity differences.

Intensitätsstereofone signals can be obtained by

• Distributing mono sound sources with panoramic dishes ( pan pots ) of a mixer
• Microphone recordings with two closely superposed microphones in an XY stereo system, MS stereo system or Blumlein stereo system.

The intensity stereophony was in the past, especially in radio due to the Monokompatiblität the predominant method: Superposition of the channels arise in this case due to the phase equality no comb filter effects.

Mixture of mono signals

The main processing means for mono signals is the mixer that allows you to place any Hörereignisrichtung for phantom sound sources on the stereo - speaker basis. The intensity stereophony is said to have the best localization sharpness. This simple assembly of mono sound sources to a stereo panorama is also the name Knüppelstereofonie. For intensity stereophony includes the Polymikrofonierung that works with completely separate mono microphone signals and their phantom sound sources are placed on the speaker base on pan control to the desired Hörereignisrichtung. This is the usual recording technology in popular music.

Microphone Systems

One of the main microphone system for the generation of stereophonic audio signals is composed of two microphones.

For all running timeless stereo microphone systems, the distance between the membranes in the ideal case with zero would. Since this is not possible, the microphones are located as close as possible to each other vertically. It also follows that a clean intensity stereophony is only possible if the sound sources are to some extent in the horizontal plane of the microphone system.

The differences in intensity of the stereo channels are obtained by utilizing the microphone directivity. In the two used most often directed pressure-gradient microphones come with directional characteristics between width cardioid and figure eight, but also pressure omnidirectional microphones are used.

XY Stereo System

The XY stereo system consists of two vertically superposed microphone capsules with cardioid polar pattern, which are rotated by about 90-180 ° apart. In practice angulation of at least 120 ° are used, so that the system can be positioned in front of the orchestra ( see also in particular XY stereo system ).

Due to the negligible horizontal distance between microphone and the directional characteristics arise when squaring the XY microphones depending on the direction of sound incidence angle frequency- neutral level differences between the signals of the two microphones. Through the axis angle between the microphones, the receiving area of the stereo microphone system is determined. This coincidence microphones (stereo microphone ) thus act as acoustic panoramic regulator. It also leads to recording with the largest localization sharpness; see links.

MS stereo system

With the XY recording technique mathematically equivalent to the MS- recording technique (MS = mid - side), in which the S- signal ( directional signal ) generated by a sideways figure-eight microphone. Next to the sound source, a microphone (center ) signal can be directed with arbitrary directivity. Between the microphone capsules, the smallest possible distance should be - which is ideally zero. A digital or analog circuit converts the mid -side to left-right signals.

The Blumlein stereo system provides two crossed by 90 ° aft microphones.

Ideally the microphone capsules are arranged as close as possible above one another. The Blumlein technique is suitable for all real pressure-gradient with the directional characteristic of a figure eight. Compared to other methods of intensity stereophony the Blumlein method is distinguished by particularly good space rendering and wide stereo base.

Pure intensity stereophony

In the pure intensity stereophony working without time lag. A level difference between Δ L = 16 and 20 dB leads to a Hörereignisrichtung of 100%, which fully from the direction of a speaker. Mean arithmetic value Δ L = 18 dB. See: (PDF, 117 kB) The generated interchannel level differences Δ L between the loudspeaker signals are not consistent with the level differences ILD ( Interaural Level Difference) to be confused, the result at the listener's ears as ear signals.

A sound recording with a main microphone system is supplemented frequently still by spot microphones.

To control the stereo signals L and R, which should arrive in the intensity stereophony with the same phase, a phase indicator ( correlation meter ) or a goniometer can be used.