Roland Jupiter-4 Compuphonic

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"'The synth's oscillators are switchable between sawtooth, square and square with PWM waveforms. and include a sub-oscillator and noise generator. All 4 oscillators can be stacked together for a fat, monophonic sound. In the filter section, the Jupiter-4 offers a hi-pass VCF, as well as a resonant low-pass filter. There are two ADSR envelope generators - one for the VCF (invertable) and the other is for VCA. The LFO features sine, square and ramp up/down waveforms, with sample/hold. It can be routed to the VCO, VCF, VCA or PWM. The Chorus button doubles the fatness of the synth sounds...'

The Roland Jupiter 4 was an analog synthesizer manufactured between 1978 and 1981. It was notable as the company's first self-contained polyphonic synthesizer, and for containing digital control of analog circuits (termed "Compuphonic" by Roland), allowing for such features as programmable memories and voice assignment modes.

Priced at around US$2,000, it was cheaper than polyphonic machine from its competitors (such as the Sequential Circuits Prophet-5 and the Oberheim OB-X) however it did not sell well in comparison. (These poor fortunes were reversed on the release of its successor model in 1981, the popular Jupiter-8.)

The Jupiter 4's basic architecture was 4 identical voice cards, each with a VCO (with sub-oscillator), resonant low pass VCF (which could self-oscillate), and VCA. Modulation included an ADSR envelope and LFO. The LFO, routable to oscillator pitch, pulse width, filter cutoff and amplifier, was notable for being able to reach audio frequencies, allowing for crude FM and AM synthesis.

The Jupiter 4's two most distinctive features were provided by virtue of its "compuphonic" digital control of the four voice cards:
* An arpeggiator, with a choice of up, down, up/down, or random mode.
* Four voice assignment modes, which, as well as simple 1VCO-per-voice polyphony, included the ability to effect 4-VCO unison when one key was pressed, 2-VCOs per voice when two keys were pressed, and 1-VCO per voice when three or four keys were pressed.

The final signal path also included a simple high pass filter and a stereo chorus effect. The Jupiter 4 had 10 preset sounds and also featured 8 memory locations for user-created patches.

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."