One of two "synth on a chip" integrated circuits produced by Curtis Electromusic in the late 1980s. The 3394 contained everything needed for a basic voice circuit: a VCO with triangle, sawtooth, and pulse, a four-pole lowpass VCF, and a VCA. Because the 3394 was intended to be interfaced with a microprocessor system, the VCO was not precisely calibrated or linearized; it was assumed that the synth's auto tune routine would take care of setting the scaling for each VCO in the system. However, the VCOs were internally temperature compensated with a built-in tempco.
Many parameters were controllable via external control voltage inputs. An unusual feature of the 3394 was that the VCO's triangle waveform could be routed to the VCF's cutoff frequency, providing a sort of frequency modulation effect internal to the chip.
Sequential Circuits was the main user of the 3394; it appeared in several of their later models, including the Six-Trak and MAX. Simmons used it in some of their drum synthesizer models. Doepfer used new-old-stock 3394s in the original version of its Dark Energy synth.
The Curtis 3396 is a somewhat similar IC model, differing mainly in that it requires an external timing oscillator; it does not contain a VCO.