The Korg Mono/Poly (MP-4) is a 44 key "mono-polyphonic" analog synthesizer manufactured by Korg from 1981 to 1984. This keyboard is the sister synthesizer to the Korg Polysix. It has four highly stable voltage-controlled oscillators (VCOs), a 4-pole, self-oscillating low pass filter (LPF), several modulation capabilities and pseudo-polyphony (paraphony).
Features include four voltage-controlled oscillators (VCOs) with tuning, footage (16, 8, 4, 2), waveshape (triangle, saw, pulse-width, and pulse-width modulated), and amplitude. The first oscillator is the master oscillator as far as fine tuning goes. Two direct modifiers to the VCOs are a detune control that only affects oscillators 2 and 4, and a Pulse Width control that goes to cancellation either side of 50% phase symmetry of a square wave; pulse width can be routed to MG1, MG2, or voltage-controlled filter (VCF) envelope.
There is one independent noise generator with an amplitude control (frequency and shape is modified by the VCF). There is one 24/db octave exponential low-pass VCF with resonance, scaling and invertible envelope control shared across all four VCOs. One voltage-controlled amplifier (VCA) envelope with triggering and dampering controls is shared across all four VCOs. There are two low frequency modulators: MG1 controls VCO Pitch/Pulse-width, 'EFFECTS' and VCF cutoff; MG2 controls the tempo of the arpeggiator, and Pulse-Width.
There is one arpeggiator with on/off/latch control, up/down/up-down pitch control, and 1/2/full keyboard control (44 notes). The arpeggiator can cycle through each oscillator in POLY mode, or all four at a time in MONO. There is an 'EFFECTS' section which includes VCO frequency modulation (X-MOD) with hard-sync control, and a frequency modulator with which the frequency of the modulator can be altered by the VCF envelope or MG1. For both modulators there is the option of single modulation of all oscillators, or two carriers, and two modulators (using the VCOs).
Controller Interfaces are external inputs/outputs for CV/Trigger, VCF and VCO mod inputs, arpeggiator, portamento, and the pitch/MG1 mod wheels can be assigned to control VCO1 pitch, pitch or the filter. Bender goes to 2.5 octaves +/- for Pitch and full range for VCF cutoff. There are 5 different oscillator assignment modes: 'Hold' drones the oscillators until force dampered or Chord Memory is activated; 'Chord Memory (MONO)' allows 2-4 oscillators (VCOs) to be set to any arrangement across 44 keys (for example, in organ or rave chords); 'Unison (MONO)' stacks all 4 oscillators; and 'Unison/Share', which defaults to Unison with one note played, but divides the oscillators across the notes as 2 or more are played. Poly is without explanation, and oscillators always play in sequenced order from 1-4.