Just curious -- on the DGX-670, is there a switch or control to switch from DSP slow rotary to DSP fast rotary and back again, on the fly while playing, which would activate the acceleration and deceleration/ramp up and ramp down effect? I'm sure it has DSP rotary speaker effects, but does it have a way to easily push a button and automatically get the speed-change effect from one speed to another?
For example, the PSR-E453-473 have the DSP rotary effect, and you can change the speed with one of the live-control knobs, but you must accelerate and decelerate it manually, by gradually turning the knob one way or another. This, of course, requires using your left hand for several seconds to simulate this effect by gradually turning a knob, when then takes away from playing the keyboard with your left hand.