The cut-up on an organ pipe affects not just the volume (which is
primarily a product of the scale and the wind pressure), but the way
the pipe speaks and the timbre of the sound as well. I can't tell you
the exact effects of the process, but a pipe organ voicer would be quite
familiar with it.

How to achieve a tremulant on the kind of instruments germane to this
site is also beyond me, but on a pipe organ, an adjustable mechanism
is used which varies the air pressure fed to a given rank of pipes --
well, except for some Austin pipe organs which use rotating "paddles"
mounted in front of the pipe mouths.

Dennis Steckley