[linux-audio-user] MIDI keyboard

[Chuck Martin]

On Tue, Mar 15, 2005 at 01:36:10AM -0500, John Check wrote:
> You wouldn't be able to do rotor inertia directly with the wave table,
> One would need a little bit of intelligence riding whatever modulator one 
> used. You could bind the LFO frequency to the mod wheel or other controller
> and push it by hand (foot).

Actually, the Leslie rotary speaker effect is a bit more involved than
that, and is difficult to get right.  I used to repair electronic organs,
and I know how the Leslie speakers work, and to get a realistic Leslie
sound requires that you first separate the sound into highs and lows with
some kind of crossover, and then process each of these separately.

When processing the sound, you then need to have a separate LFO for the
lows and the highs, and the inertia effect needs to be greater on the
low frequencies.  What I mean by this is that when you switch the speed
from slow to fast, or vice versa, the speed should change quicker on the
highs (I'd guess about a second, although I haven't timed it), while the
speed change on the lows should take longer (several seconds, but again,
I haven't timed it, so I can't be precise).

Also, the changes that take place as those rotors are turning are very
complex, and depend to a great extent on the room as the sound bounces
off of the walls, ceiling, floor, etc.  It isn't a simple vibrato, or
vibrato + tremolo + filter modulation.  There's a doppler effect that
effects the sound differently depending on whether it's direct or
reflected.  Remember, the doppler shift on a source that's moving away
from you is opposite the doppler shift on a source that's moving toward
you, so the reflected sound from the back wall would be shifted in the
opposite direction from the sound coming to you directly, and the shift
from a side wall would be different from either of those.

I've heard very few Leslie simulators that even come close to sounding
like a real Leslie.

Chuck