This is the ability for parts of a synthesizer to be able to modulate other parts of the synthesizer. The synths with most cross-modulation abilities are modular synths, which actually use patch leads to plug different modules into each other, so any output can be plugged into any input....
SH-101
The Roland SH-101 is a monophonic synthesizer, featuring a 2 1/2 octave 32-note (F-C) keyboard in a light, plastic
case. It was designed as a strap-on synth with an optional modulation attachment that stuck out like a guitar neck. It
can run on batteries and it came in a number of exciting colors. The SH101 was pre-MIDI, but it has CV (1
volt/octave cv) and gate inputs in the back. It features one VCO with separate levels for each waveform, saw,
square, pulse, Pulse Width Modulation (PWM), and suboscillator. PWM can be set at one level or can be controlled
by the EG or the LFO. The VCF is self-oscillating (resonant) and can be modulated by the envelope generator, the
LFO and the keyboard (keyboard tracking). The Envelope Generator (EG) is ADSR and can be triggered by the gate
or the LFO. The LFO can be set on triangle, square, random (sample-and-hold), and noise. The VCA can be
controlled by the EG or the Gate. The SH-101 also features a very primitive arpeggiator and sequencer as well as
portamento.