The SD-1 comes from a long line of Ensoniq’s evolving TransewaveTM wavetable digital synthesizers. It began with Ensoniq’s earliest synthesizer, the ESQ-1. That led to the SQ-80, then the VFX and VFX-SD (the latter featuring an on-board sequencer) and then to the SD-1 (and it eventually led to the Fizmo). The SD-1 allows for additive synthesis using waveform modulation, a sort of wavetable synthesis. This puts it into a unique class of digital synthesizers along with the PPG Wave series and Waldorf Microwave series.