Microphones and miking techniques - Stereo miking techniques: Introduction

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The aim of these techniques is to reproduce a stereo sound field, and therefore they require the use of two or more appropriately placed microphones. These techniques have been sub-divided into three groups: coincident microphones, near microphones and distant microphones, each of which has its own characteristics with different advantages and disadvantages, each described in the following section.

10.14.1. Coincident microphones

Here we'd use two microphones positioned in the same spot. For this reason this pattern can record amplitude and not phase differences between the two microphones since the sound reaches the two diaphragms simultaneously. This makes this kind of technique mono-compatible and therefore ideal for radio and television work.



10.14.2. Blumlein technique

Two microphones with a figure of 8 polar pattern are used, named 1 and 2, and are positioned as shown in the following diagram:

Microphones and miking techniques - Blumlein technique

Blumlein technique

This technique's stereo effectiveness is based on the presence of reflections that get picked up by the posterior lobes of two microphones.

The angle between the two diaphragms is fixed at 90 degrees. Microphone 1 points towards the left hand-side of the sound field whilst being stimulated by reflections issuing from the right side. The exact opposite takes place with microphone 2. This technique is particularly effective in environments with good acoustics, in which the presence of reflections are a determinant factor in the colouring of sound. On the mixer the two sounds are kept separate and routed straight to the outputs.



10.14.3. XY technique

This technique involves two condenser microphones with a cardioid polar pattern at an angle which goes from 90 to 110 degrees (an excessively wide angle could create a hole in the stereo image).

Microphones and miking techniques - XY technique

XY technique

At the mixer the two signals are kept separate and routed straight to the outputs.



10.14.4. MS technique - Mid Side

This technique involves two microphones, one with a cardioid polar pattern and one figure of 8, positioned as follows:

Microphones and miking techniques - Mid Side technique

Mid Side technique

The cardioid microphone reproduces the signal issuing from in front of it, whilst the figure of 8 reproduces the lateral signals. To decode these signals on the mixer, the following scheme is used:

Microphones and miking techniques - Decoding of Mid Side signals

Decoding of Mid Side signals

The central signal is reproduced exactly as it is, whereas the one coming from the figure of 8 microphone is split into two. One part is sent to the left loudspeaker and the other is inverted in phase and then sent to the right loudspeaker, after they have both been attenuated by 3 dB (this compensates for the fact that the signal had at first been divided into two). Mono-compatibility is guaranteed by the fact that by summing up the two signals, the one coming from the figure of 8 microphone is cancelled.

The amplitude of the sound-image is controlled by panpot controls [Panpot ] which operate on the two lateral signals.










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