An input into part of the synthesizer that allows that bit to be modulated by another part of the synth. For example there is a control input in the amplifier which controls the level of amplification. If a very slow sine wave (an LFO) is patched into this input then the sound will slowly get louder and quieter. If an LFO was patched into the control input of the oscillator instead, then the sound would go higher and lower in pitch....
OB-Xa
An enhanced version of the OB-X, the OB-Xa also was "available in four-, six-, and
eight-voice configurations, offered 32 program memories, polyphonic portamento, and
polyphonic sample-and-hold", and in addition to that, it "offered the ability to split the
keyboard, or double up the voices so that two voices would sound for each key that was
depressed."