- I31 Base Width Control Unit
- M/S Stereo Direction Mixer with Base Width Control and Elliptic Equalizer for 4U Frames
- Using the I31 with two microphones and pre-amplifiers, it is possible to make an M/S recording. This technique offers good stereo imaging with the added benefit of excellent mono compatibility.
The functional principle of the base width control:
- The device moves a stereo signal by means of a matrix of the L-R format in the MS format. While in the normal stereo format both channels are transferred to the left and right channels separately, the MS principle works differently. The M, or middle channel transfers a pure mono signal, while the S, or side channel contains all the directional information of the stereo signal.
- With a stereo signal in the MS format, regulations are possible which are not normally possible. First of all, the stereo parameters base width and direction concerns this regulation. (Please read the description of the direction mixer W731 in the V700 series.) By regulating the level of the side signal the base width of the stereo-signal changes. If the S signal is muted, only a mono signal is left. If the level of the side signal is increased, the base width increases. A direction regulation is also possible in which one regulates the side signal against the middles signal. The result that arises is similar to that of using a pan pot or balance control. Except that these controls turn off the opposite side of the signal when they are turned fully to one side. The direction regulation at the MS level on the contrary gets all signal components of the input signal. In the extreme positions L and R appears as a mono signal that corresponds to the addition of both input channels. The resulting signal however, will be narrower.
- The application of this base width control device presents outstanding possibilities for the influencing of the spatial image of stereo signals. With the base wide regulation one can reduce or increase the width of the signal. The signal width can then be shifted with the direction fader on the stereo basis. With it the direction mixer becomes the ideal device for the distribution of stereo signals in the mix. So very attractive spatial sounds can be constructed easily.
The elliptic Equalizer
- The elliptic equalizer reduces the base width from an adjustable lower border frequency. This is used to solve mono compatibility problems that are caused by time delay effects and phase displacements in the low frequency range. The side effect of widening the base is increased out of phase components in both stereo channels; therefore, the problem of the mono compatibility increase as the base is widened. Naturally the biggest part of these signal components appears on the basis of the level statistics in the low frequency range. An adjustable, frequency dependent, cross talk is produced between the stereo channels. The range applies from 40 hertz to 3150 hertz for 15 dB cross talk.
- Setting the cross talk frequency at or below 300Hz cause no detectable changes in the width of the stereo signal, with frequencies above 300Hz changes become audible. Which settings are meaningful, one must judge according to hearing by change of the fader position and test of the mono compatibility. The elliptic equalizer is independent of the direction mixer.
- The base width control module can be used with any 4U Integrator frame.