Test Reviews of Pro Audio Gear and Mixing Consoles

Analog Stereo Mastering Processing Gear
adt-audio ToolMod MS and BM

Translation of a test review from German Studio-Magazin by
Dieter Kahlen

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The stereo module TM130 combines M/S matrix, stereo direction controller and an elliptic equalizer. The input of these devices can be driven by left-right stereo signals as well as by M/S input signals. Experts appreciate the extremely interesting possibilities of a stereo direction control device ever since; for example to distribute stereo sources on the stereo base while mixing. Such a circuitry requires M/S signals that are usually converted from a left-right stereo source by an input matrix. If the unit is used for stereo microphones in M/S mode, the input matrix is switched off by the ‚Input M/S’ pushbutton. The base control of the direction controller section is actually a level control of the ‚S’ signal that contains the stereo information of the signal; therefore the level of the ‘S’ channel represents the base width, while the ‚M’ signal, which contains the mono components of the signal remains unchanged. At the center position of the control the base width is not changed; all to the left the ‚S’ (=side) signal is muted and only the ‚M (=mono) signal remains. All settings of the base control pot to the right result in an artificial enhancement of the stereo base width, due to the relative gain of the ‚S’ signal related to the ‚M’ signal.

The  M/S Matrix TM130

In order to maintain the mono compatibility that often suffers from base width enhancement, the elliptic equalizer can be used to reduces the base width below an adjustable frequency. This can be done without an audible reduction of the stereo width since human ear is not able to locate signals of a frequency lower than 300 Hz.

Another useful tool of the TM130 is the direction control that let’s you move a stereo signal on the stereo base. In difference to common pan pots or stereo balanced controls, the direction control will not mute the opposite channel when the control is set all to the left or all to the right. In these positions, the circuitry generates a mono signal that contains both input channels.

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