A "synth on a chip" integrated circuit produced by Curtis Electromusic in the late 1980s; it was one of the company's last designs. The 3396 implemented the same basic idea as the 3394; it contained waveform sources, a VCF, and VCA capaility all in one IC.
The most unusual and unique feature of the 3396 was the way that it generated waveforms for synthesis. The IC has no onboard oscillator; it must be driven by an external oscillator of some sort, feeding a square to the 3396. The frequency of this input determines what note the 3396 plays. The idea was that the 3396 would be used in a microprocessor-controlled synth and the desired input frequencies to each 3396 would be generated by a processor-controlled divide-down of a master high-frequency oscillator, perhaps the same oscillator used to generate the CPU clock for the microprocessor.
What the 3396 does contain is two sets of waveshaping circuits, driven by the external oscillator. The various wave converters can produce triangle, pulse, and sawtooth waves depending on which control voltages are applied to the converter inputs. It actually is also capable of producing a variety of highly complex waveforms by tweaking the converter inputs properly, but this capability was seldom exploited in synth designs that used the 3396. The two sets of waveshapers can be driven by two separate timing oscillators, allowing signals of two different frequencies to be generated within the IC.
A voltage-controlled mixer feeds a mix of the two generated waveforms to a conventional four-pole lowpass VCF. The output of this then goes to the final VCA section. The 3396 is unusual in having two VCAs in series; the first one accepts a linear control voltage, and the second one takes an exponential control voltage.
The best-known synths to use the 3396 were the Oberheim Matrix-6 and Matrix-1000. Two versions of the 3396 were made in different packages; these are referred to as the "wide" and "narrow" body versions. The narrow-body version is easier to find today. The Matrix-6 requires the wide body version, but an adapter is available allowing it to use the narrow body version. Electrically, the two versions are identical.