Quadra - another successful "chimera" by ARP, which can be safely included in the top 100 analog synthesizers. This time four instruments fit one housing at once, which is obvious thanks to its name. Polyphonic section of strings, monophonic bass and a polyphonic synthesizer were taken from Omni, Odyssey added its expressive lead to the instrument.

The management of all four instruments became possible owing to the use of the intel 8748 microprocessor, which integrated the components, and also allowed saving the settings of the synthesizer in the presets.

Working with the bass synthesizer takes place within the first two octaves of the keyboard. There are two sound modes ("elec bass" and "string bass") that can work simultaneously. This section includes an independent voltage-controlled low-pass filter (LP VCF) with a slope of 6 dB per octave with the cutoff frequency subjected to a simple envelope generator control with release adjust.

The polyphonic section of strings, as well as in Omni, is based on the method of splitting down, which was widely used for constructing polyphonic sounding in electro organs. Only attack and release time are available among the settings. The section comprises an independent chorus effect block for sound saturation.

The polyphonic synthesizer section produces notes achieved by converting a meander from a string section to a saw. The section features independent blocks:

VCF (ARP4075) with adjustment of resonance, cutoff frequency, modulation depth by LFO and envelope generator.
VCA is controlled by the envelope generator block.

ADSR – envelope generator.

The solo (lead) synthesizer uses two voltage-controlled oscillators (similar to those used in Odyssey and ARP2600) to produce its sound, which produce a sawtooth and square wave. For each generator there’s a pitch tune available, which allows you to get a detuned sound, and set an interval for the oscillators. Pulse width and frequency modulation (PWM and FM), vibrato mode in LFO are available for oscillator section. Independent LP VCF (ARP4075) unit offers adjustment of resonance depth, cutoff frequency and depth of envelope generator influence. The envelope generator is presented as ADR here.

In the mixer section, the level of each section and the master volume can be set, after which the signal enters the chorus phase shift block. For the phaser speed and resonance controllers are available.

The Quadra keyboard encorporates an aftertouch recognition technology within the three upper octaves, the signal of which can be routed to control the pitch or filter modulation.

For the synthesizer lead section there is an arpeggiator and a system for memorizing intervals (the interval is assigned for each key making the second VCO to be tuned respectively).

There are 16 memory locations to save the basic settings.

Among the famous artists who used ARP Quadra, there are 808 State, Duran Duran, The Human League, Genesis, New Order, Kansas and Weather Report.