Tuesday, October 20th, 2020 09:50 am
The Jupiter 4 Compuphonic (known to most of us as just the Jupiter 4) is a four-voice polyphonic synthesizer with
an arpeggiator and a 49-note (C-C) keyboard. It has 8 user-programmable memory locations and 10 preset patches
with names like "Piano" and "The Force". The buttons for patch changes are in the front of the keyboard, underneath
the keys. Each voice consists of a single VCO with sawtooth, square, or square with Pulse Width Modulation
(PWM) and a suboscillator that can be switched on or off. There is also a noise generator that can be switched on
and off. Like the suboscillator, it has no level control.
The Jupiter 4 can be put into mono mode which stacks all 4 oscillators on each note, creating a very thick, although
monophonic, synth. The filter section consists of a high pass filter and a low pass resonant filter. The Jupiter 4 has
two ADSR envelopes, one for the filter which can be inverted, and another for the VCA. It also has one LFO,
switchable between sine, square, ramp up and ramp down waveforms. The LFO can be routed to the VCO, the VCF,
the VCA, or PWM. Although some say that the LFO rate on the Jupiter 4 is the slowest of any production keyboard,
it also can modulate up into the audio frequencies (around 100 hz), making it very flexible. Only the filter can be
modulated by a sample and hold function of the LFO labeled as "VCF mod" in the filter section.
The Jupiter 4 has a built-in chorus, a single on/off switch labeled "ensemble". Its arpeggiator is a fixed range
running the length of the keyboard. However, there is a click input to sync the arpeggiator to an outside source. The
click input can also be used to trigger filter modulation. This input and a cv input for the VCF were the only
interface available with the Jupiter 4. It has no keyboard cv/gate input. It is possible to overdrive the Jupiter 4's
VCA. When you do this a little light comes on to let you know.
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