Roland MC-4 [1981] An early microprocessor-based music sequencer that was the successor to Roland’s MC-8 (the first microprocessor-based digital sequencer in 1977). The MC-4 can be programmed using the ten key numeric keyboard or a synthesizer keyboard using the keyboard's control voltage and gate outputs. MIDI wasn’t always around - and before it was invented by Dave Smith, manufacturers had their own proprietary standards to synchronize instruments, such as DIN sync, Digital Control Bus (DCB) and CV/gate - which I’m sure you’re familiar with, especially if you’re in the world of modular synthesis. MIDI is digital, whereas CV note information is analog. With MIDI, notes are sent in two separate MIDI messages - one activates the note at a certain pitch and velocity, and second is sent later on, when it's time to turn the note off. As for CV/gate the CV (control voltage) typically controls pitch and the gate signal controls note on-off. The MC-4 has an output patchbay with four channels of outputs able to control four separate synthesizers via CV-1, CV-2, Gate and MPX (multiplex). It has three modes of operation. They include Play, Edit/Data Entry and CMT. The latter option for data transfer to and from cassette. Roland made the MTR101 tape machine to allow this, and since it was a custom device, it could be controlled direct from the MC4 keypad. There is a pretty cool vid of this in action via @alexballmusic’s YouTube channel! Highly recommend. Notable users include Aphex Twin, The Human League, Vince Clarke, Suzanne Ciani and more. References: Loop Pop, Sound Synthesis and Sampling, Wiki, Photo - Music Technology 1987.