From the manual , in 5.3 The Filter and its Envelope
The two “Keyboard control” switches allow the use of a key follow at the filter cut-off frequency.
When they are set to the “OFF” position, no key follow is connected.
When the first is “ON”, the key follow allows the modification of the cut-off
frequency by a major third for an octave.
When the second is “ON”, the key follow is of a fifth for an octave, and when both
are “ON”, the filter cut-off frequency exactly follows the keyboard. It should be noted the pivot note is F0.
From the manual at section 5.1
The “Osc. 2 Control” switch allows to activate and deactivate the command of oscillator 2 by the keyboard.
The “Osc. 3 Control” switch is for activating and deactivating the command of oscillator 3 by the keyboard.
The “Oscillator Modulation” switch modulates oscillators 1,2 and 3 via oscillator 3 with an amplitude depending on the modulation wheel. If we don’t want to have oscillator 3 modulate itself, we need to deactivate the switch.
I too was wondering about them just today, and looked them up.
