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Stereo recording techniques

Stereo Recording Techniques (570 KB)
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6. Equivalent directional characteristics combinations

Physically seen, the XY and MS recording techniques are equivalent under certain circumstances. As we have already seen, there is a simple relation between the signals L, R, M and S; they can be converted into each other. this conversion is also called stereo conversion.

M = L+R	L = M+S
S = L-R	R = M-S

Since M and S can be converted into L and R in the same way as L and R into M and S, both conversions can be done with the same device (sum-difference transformer or differential transformer).
Due to this equivalence, certain XY-combinations correspond theoretically to certain MS-combinations. But in practice one will find some differences between equivalent XY-MS combinations. Since the microphone voltages are frequency dependant, all MS-combinations reproduce the higher frequencies better in the range of the symmetry axis for example, the XY-combinations better in the lateral ranges.

Coincident microphone

Fig. 12

Fig. 13

Definition of terms for upright standing coincident microphones

1.	fixed capsule	channel I	delivers in XY-Technique: L signal delivers in MS-Technique: M signal
	System I (below)

2.	revolving capsule	channel II	delivers in XY-Technique: R signal delivers in MS-Technique: S signal
	System II (above)

3.	angle of displacement:	angle at which the main sensitivity directions of the microphone capsules are turned away from the symmetry axix (mechanically)
		Adjustment:	XY-combination: freely selectable MS-combination: M = 0° ; S = 90°

4.	recording range:	range, that at replay will be represented inside the "Stereo Basis"

5.	recording angle:	angle that includes the recording range

Stereo Recording Techniques (570 KB)
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Stereo recording techniques