A filter filters out certain frequencies in the sound. There are four main types: a low-pass, high-pass, band-pass and notch, which are covered elseware in the glossary. Filters have two controls - the frequency control selects at which frequency the filter should start operating and the resonance control creates a peak just before the bit where it starts filtering out frequencies. This is used to create acid-type sounds....
Quadra
"The name Quadra is derived from the fact that the instrument is actually four
separate synthesizers in one microprocessor-controlled system. This instrument
gives the musician the ability to write, edit, store, and activate the sounds of four
synthesizers in live performance. [It is sort of like a combination of an Omni and
an Odyssey] "The Quadra's four sections are: a bass synthesizer, string
synthesizer, polyphonic synthesizer, and two-voice, touch sensitive lead
synthesizer. A stereo, voltage controlled phase shifter is also included, designed
for the Quadra's special requirements. "The bass synthesizer can be
programmed to control the two lower octaves of a five-octave split keyboard,
ranging from electric to string bass settings. "The string synthesizer produces the
rich, deep string sounds for which ARP is famous, and can be used with the built-
in phase shifter for exceptionally dramatic string choruses. "The poly/synthesizer
section provides the musician with a quick change of envelope control
parameters at a touch of a switch. Brass, Piano, and synthesizer sounds can be
processed through the phase shifter, sample/hold and other circuits for a variety
of polyphonic synthesizer and keyboard effects.
["It was a top-octave subdivider system (basically an electronic organ) with a
single VCF, VCA and ADSR for all notes. All notes passed through a single
set of envelopes with the first keys struck in a chord triggering the envelope.
Fine for block chords, but a "strummed" chord was impossible. Also it read
the KB CV to the filter off the highest key pressed, making for funny results
played two handed chords at once. The Quadra was about two or three years
too late to make a difference, as both Sequential Circuits and Oberheim had
real programmable polyphonics on the market by 1978." ----Joseph Swails, a
former ARP salesman]
"The lead synthesizer section is actually a two-note, lead-line variable
syntheszier, with pressure-sensitive (second touch) control of dynamics over
three octaves, and full five octave range when the bass synthesizer section is not
in use. "The Quadra's lead capability includes twin-channel portamento and,
coupled with a microprocessor, allows intervals and octaves to be programmed
from the keyboard in real time. A built in sequencer permits instant sequential
effects which follow every key depressed. The sequence can be memorized and
held while the keyboardist plays additional string and polyphonic lines on top of
the latched sequence. [Unfortunately there is no external sync for the
sequencer.] "At the heart of the Quadra is a computer programmer, a device
which unites preset and variable synthesizer technology. Prior to a performance,
the musician sets up the desired sounds in each section and stores these sounds
into any of the 16 programmable positions. The sounds are memorized and can
then be recalled by touch. [Memory settings let you know which sliders are
active. It does not set the positions for you, but rather, it just lets you know which
ones to move.] "Each section of the Quadra is individually programmable and
mixable through the output mixing controls centrally located on the control panel.
Additional synthesizers can be interfaced with the Quadra through ARP systems
interface jacks. Pedal and footswitches control inputs for a variety of Quadra
functions are easily acessible on the back panel."
In addition to the separate outputs for each synth, there are separate CV/gate
inputs for the Bass and the lead synth voices, and an additional seven Control
Voltage inputs.