In 1978, the first microprocessor-controlled analog synthesizers were created by Sequential Circuits. These used microprocessors for system control and control voltage generation, including envelope trigger generation, but the main sound generating path remained analog. The MIDI interface standard was developed for these systems. This generation of synthesizers often featured six or eight voice polyphony. Also during this period, a number of analog/digital hybrid synthesizers were introduced, which replaced certain sound-producing functions with digital equivalents, for example the digital oscillators in synthesizers like the Korg DW-8000 (which played back PCM samples of various waveforms) and the Kawai K5 (waveforms constructed via additive synthesis). With the falling cost of microprocessors, this architecture became the standard architecture for high-end analog synthesizers.