Split live histogram mode (separate visualization of system monitor vs microphone input loudness graphs)

[nekohayo]

During recording, I often find myself wanting a visual confirmation that I am recording from the correct inputs, and that the loudness and noise levels are acceptable and well balanced.

As such, I would love if it was possible to optionally have two live histograms (either one on top of each other, or side-by-side split view).

This would let me see, for example, that my microphone is much quieter than the other person's microphone, or that my noise level is polluting the recording when I am not talking and that I should mute myself (a toggle mute button on each histogram half would actually be amazing to have, too).

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This enhancement request is different from #222 (which is about separate streams recording; in my case I want both to be combined in a single file, but the live visualization to be different) or from #236 (which is about helping to pick the correct device before starting recording).