The Quadra Ensemble Synthesizer has 16 polyphonic voices and can be played over five octaves. It has four sections: bass, string, polysynthesizer and lead synthesizer. It was intended to combine the advantages of earlier Arp products such as the Omni and the Odyssey in order to help the ailing company back to success. Sales remained limited, however, as there was strong competition from the Sequential Prophet-5 and the Oberheim OB-X, among others. At least it received some attention from users such as Tony Banks from Genesis. It only gained its current cult status as one of the best analog synthesizers decades later.
The Quadra's bass section with its freely tunable VCO is monophonic and features electric bass and string bass. Foot positions 16 and 8 can be combined. The string section is similar to the Omni; violas and violins can be added via foot positions 4 and 8. Bass and string can be played simultaneously. The polysynthesizer section shares the tone generator with the strings. It has an ADSR envelope. Buttons determine whether attack, decay, sustain and release are controlled by presets or set individually. There are 16 memory locations for this, which are controlled by an 8048 microcontroller. Cutoff and resonance are also influenced via ADSR. As with organs, polyphony is achieved by frequency division and not by assigning individual envelopes to each note. The lead synthesizer has two voices with two VCOs and can be played over all five octaves as long as the bass is switched off. It offers sawtooth and square wave, the filter curve is modulated by the envelope using a fader, and it can be played with velocity sensitivity. An output mixer controls the sound of the four sections. The phase shifter is used to set effects for all sections individually. (Source: Amazona)
