User's Manual

4. HOW ANALOG SYNTHESIS WORKS
If you’ve never programmed an analog synthesizer before, here’s a basic explanation of
how the different controls of the Jupiter 8 relate to each other. It may seem complicated
at first glance, but actually the controls on the top panel are arranged in a very logical
way. Once you understand these basic concepts you’ll be able to make your own sounds
on almost any analog synthesizer, since most classic analog synthesizers use a similar
structure.
4.1. What each module does
4.1.1. VCO
Stands for voltage-controlled oscillator. This is the fundamental sound source of analog
synthesis. Each VCO generates an audio signal based on a DC voltage from the keyboard,
combined with modulation sources; the higher the voltage, the higher the pitch. That voltage
and pitch can be changed not only by the keyboard, but from envelopes, low frequency
oscilators (LFOs), even another VCO.
In the Jupiter 8, each voice has two VCOs (VCO-1 and VCO-2). Since it has up to 16-note
polyphony, there are actually 32 VCOs in the instrument. Part of the unique sound of the
Jupiter is its ability to stack all those VCOs onto whatever keys you’re pressing. See Unison
Detune [p.19] for details.
In analog synthesis, it’s important to realize that a VCO is always “on”, generating signal, like
a test tone in a laboratory. (Press the HOLD button to see this “infinite sustain” characteristic.)
To be musically useful, the audio from the VCO has to flow through other modules (in the
Jupiter, a VCF and VCA) that will “shut it off” (sooner or later) when you take your fingers
off the keyboard.
4.1.2. VCF
Stands for Voltage-Controlled Filter: If VCOs are the heart of analog synthesis, VCFs are its
soul. A VCF is a powerful and dynamic tone control that can sweep across the frequency
spectrum in response to your playing, or simply act as a static lowpass filter cutting the
upper frequencies of the signal passing through it.
The VCF in the Jupiter 8 is a resonant low-pass filter (LPF) with a sweepable frequency
control. The CUT control, plus modulations, determines the cutoff frequency. Only sounds
below this cutoff frequency will pass through; everything above it will be filtered out at a
slope of either -12 dB or -24 dB per octave. At its lowest setting, (20 Hz), virtually no audio
will pass through the VCF. If the VCF CUT, MOD, and KEY FLW controls are at zero, no sound
will come out of the Jupiter-8. Even if the MOD control is up, if the Envelope settings are
down, it still will filter out all the signal.
Arturia - User Manual Jup-8 V4 - How Analog Synthesis Works 28