ARP Omni

The ARP Omni was a polyphonic analog electronic music keyboard manufactured by ARP Instruments, Inc. It ranks as ARP's best-selling keyboard.

Overview

The Omni featured preset, electronically generated Orchestral ensemble String voices including polyphonic Violin and Viola sounds as well as monophonic Bass and Cello. The instrument also included a monophonic Bass Synthesizer section and a polyphonic Synthesizer section. The Synthesizer section featured a 24dB/oct Voltage-Controlled Low Pass Filter (LPF); an ADSR envelope generator and a single waveform (triangle) Low Frequency Oscillator (LFO) were both routed to control the VCF Cutoff frequency. A Waveform Enhancement switch allowed selection of a square wave voice waveform vs. the default quasi-sawtooth waveform.

Voicing

The String and Synthesizer sections of the 49-note Omni utilized the Mostek MK50240 Top Octave generator IC along with divide-down circuitry; as a result, these sections were fully polyphonic, as opposed to subsequent polyphonic synthesizers such as the Sequential Circuits Prophet-5 and Yamaha CS-80 which featured dynamically allocated, limited polyphony of 5- and 8-voices respectively (although these units featured a far more comprehensive and complex synthesis architecture).

The three sections of the Omni - Strings, Synthesizer, and Bass - were all simultaneously available and mixable; the String and Synthesizer sections featured separate audio outputs on the rear panel of the unit which allowed...
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