LCR mains

Governed by: docs/design/specs/2026-09-08-lcr-mains.md

A MAIN bus can carry a third, discrete centre speaker feed alongside its usual left and right — the LCR format. This is for a room with its own centre cluster: a vocal or a centred instrument can sit in a genuinely discrete C output instead of a phantom image built from the L/R pair.

Turning a MAIN into LCR

Select the MAIN strip and open its processing view. A Format picker sits on the strip head, offering whatever this console's appliance actually supports — some consoles only ever offer Stereo, because their engine has no discrete centre output to give one. Where LCR is offered, picking it grows a third output on MAIN immediately.

If the console refuses the change, the picker shows why (the exact reason the desk gives, not a paraphrase) instead of silently staying on Stereo.

Switching a MAIN that is already mixing is an operator action with an audible consequence — every channel's image redraws through the LCR panner (below) the moment you pick it. Switching back to Stereo removes the C output and returns every channel to a phantom image.

Divergence — how much of a source is discrete

Once MAIN is LCR, every channel feeding it grows a second control beside Pan: Divergence. Pan still places a source left-to-right exactly as before; Divergence decides how much of a centred source comes out of the discrete C speaker rather than being phantom-imaged between L and R.

• Divergence at 100% (Phantom) — the default, and what an untouched channel plays: the image is exactly what it always was, with C silent.
• Divergence at 0% (Discrete) — a source panned to centre plays entirely out of C, with L and R silent for it.
• Anywhere in between reads as Phantom NN% — a blend of the two.

Divergence is a property of the CHANNEL, not of any one destination: if a channel feeds both an ordinary stereo aux and the LCR main, its one divergence value only does anything on the LCR leg — the aux hears the same channel it always did.

On a channel whose destination is not LCR, no Divergence control appears at all — there is nothing for it to do there.

The meter and the leg block

An LCR MAIN's meter grows a third bar, L C R, so you can see level reaching the centre speaker the same way you see it reaching the others. A MAIN that is Stereo keeps its usual two bars.

In the patchbay, an LCR MAIN's leg block grows a third cell, C, beside L and R — the same tap-to-patch, long-press-to-unpatch gesture as the other two, and the feed's trim, alignment delay and mute (drawn once, for the destination as a whole) apply to all three legs together. A Stereo MAIN keeps its usual two-cell block.

X-Touch: SHIFT turns the V-Pot into Divergence

On an X-Touch in MCU mode, a strip's V-Pot dials Pan by default. Hold SHIFT (the modifier key under the display) and turn the SAME V-Pot: while SHIFT is held, the turn dials Divergence instead, and the ring shows the divergence position (empty = discrete, full = phantom). Release SHIFT and the V-Pot is Pan again.

This only redirects a V-Pot that is currently dialling Pan, and only where MAIN is LCR. On any other strip — a V-Pot dialling head-amp gain, or MAIN when it is Stereo — holding SHIFT achieves nothing: the V-Pot keeps doing its ordinary job, never a write to a fact that means nothing there. SHIFT never overrides a physically held V-Pot push either — that momentary pan layer takes priority, exactly as it did before SHIFT existed.

What LCR does not do yet

This is phase 1 of a larger surround design. It does not currently include:

• No LFE, no 5.1/7.1. The format list is exactly Stereo and LCR.
• No cue/monitor centre fold. Soloing or monitoring a channel that feeds an LCR main does not yet fold its C content into the two-speaker cue bus — that crossfade is designed but not built. Until it lands, monitor what MAIN itself is doing rather than relying on cue to represent the centre image.
• Appliance-dependent. Whether LCR is even offered on MAIN depends on the console profile in use — not every supported desk models a discrete centre bus.