SPL Gemini Mastering M/S Processor

The decomposition of the stereo signal in mid (voice, snare, bass …) and side (guitars, pads, cymbals …) allows their separate processing. The center signal (Mid) is the sum of the left and right channel of the stereo signal (L+R), i.e. the “in phase” part of the stereo signal. The side signal (Side) is the difference of the left and right channels of the stereo signal (L-R), i.e. the “out-of-phase” part of the stereo signal.

SPL Gemini can also be used to enlarge or reduce the stereo image. An elliptical filter for shifting the low frequency component from the side to the mid is also on board. When the M/S button is activated, the input signal (L/R stereo) is split into a mid and side signals. The exact center position can be adjusted with the Balance control and the exact level with the Trim control. Both functions are switchable to be in the signal path only when in use.

Exclusive monitoring of the center is possible when the solo function is activated. Processors can be inserted to process the mid signal and activated with the Insert button. The side signal also has a solo function and a switchable insert for external processing.

In addition, the elliptical filter can be used to shift the bass frequencies from the side to the mid. This improves the punch and precision of low frequencies. The Stereo Width control changes the level of the side signal, with a level increase broadening the stereo image.

These two functions can also be switched on to be in the signal path only when used. All inputs and outputs as well as sends and returns are balanced using Neutrik XLR connectors. Processors can be connected to the inserts for external processing.

Especially interesting is the integration of the SPL Gemini into the Hermes Mastering Router. In this way, processing chains can be created that combine classic L/R processing with M/S processing.

The M/S encoder and decoder stages of the SPL Gemini can each be connected to an insert of the Hermes and freely positioned within the processing chain. Processors that are in a chain between M/S encoder and decoder process the mid/side signal. These processors can also easily be mono devices.

In one example, Insert Send A is routed to Gemini for M/S encoding. The mid/side sends of the SPL Gemini go back to Return A of the Hermes. Send B goes from Hermes back to the SPL Gemini to be encoded back to L/R, which flows from the output of the Gemini back to Return B of Hermes.

For example, it is possible to place the M/S encoder at processing position 3, an equalizer at processing position 4 for separate processing of the mid and side signals, and then the M/S decoder stage of the SPL Gemini at processing position 5 to generate an L/R stereo signal again.

If a compressor is now to be used as an additional device for M/S processing, it can simply be set to processing position 5 in the chain, and the M/S decoder stage would move to processing position 6 accordingly.