User's Manual

4.1.3. VCA
Stands for Voltage-Controlled Amplifier. The signal passes through this after the filter
section; controls the final output level over time. It’s the last step in the signal path. The VCA
“opens and shuts the door” on the signal based on how the ADSR controls of ENV-2 are set.
If the VCA LVL control is at zero, or if ENV-2 controls (A, D, S) are all at zero, no sound will
come out of the Jupiter-8.
In analog synthesizers, a DC voltage from an envelope generator (or other source) “opens
up” the VCA: at 5 volts the VCA is wide open, as the voltage falls lower, the volume output of
the amp is also lowered, until at 0 volts it is closed and no signal passes through the VCA at
all.
Don't be misled by the word "amplifier" here: it doesn't make the signal louder, it is a negative
amplifier with the ability to reduce the signal level below unity gain.
The JUP-8 V4 main panel consists of:
• 2 oscillators (“ VCO 1 and 2 ”) in which the second can equally be used as a
source of modulation
• 1 mixer to set the balance between the 2 oscillators
• 1 High pass filter (“ HPF “) 6dB/oct non-resonant
• 1 low pass resonant filter (“ VCF “) 12/24dB/oct
• 1 amplifier ("VCA")
• 2 envelopes dedicated to filter and amplitude modulations
• 1 LFO (low frequency oscillator)
• a MOD wheel section (LFO MOD) dedicated to the LFO in performance
4.2. Audio and modulation signal paths
The middle section of the top panel is laid out from left to right in order of the actual signal
path:
• a pair of oscillators (VCOs) generate the audio signal with a fixed set of harmonic
overtones (such as a square wave, sawtooth wave etc.),
• filters (HPF and VCF) change the tone of the sound,
• and the amplifier (VCA) changes the volume/level of the sound.
The left and right sections of the top panel contain the modulators: the Low Frequency
Oscillator (LFO) and VCO Modulator on the left, and the Envelopes (ENV-1 and 2) on the
right. These sections don’t make any sound on their own (usually), but are designed to be
“plugged in” to the signal path to change the sound over time:
• When sent to a VCO, they change its pitch (LFO for vibrato, ENV for pitch sweep)
• When sent to the VCF, they change the timbre (like a wah-wah or horn mute)
• When sent to the VCA, they change the amplitude level (LFO for tremolo, ENV to
provide the way the sound attacks and decays over time).
29 Arturia - User Manual Jup-8 V4 - How Analog Synthesis Works