The SD-1 is the follow-up to the Ensoniq VFX-SD. It has 11 notes of additional polyphony beyond the original VFX and adds a 1MB piano ROM.
Like the VFX, it can use up to 6 waveforms together in a single patch and has 11-stage envelopes. The built-in sequencer can record 12 tracks in step or realtime recording mode and can be expanded to 75,000 note capacity with the optional SQX-70 expansion.
The SD-1 contains a set of 17 transwaves that can be used for wave sequencing. Here is the transwave list:
As the top of the VFX line, the SD-1 usually commands prices significantly above a VFX-SD despite only being a minor upgrade sound-wise.
To check the ROM version of your SD-1, press and hold the PRESETS button and then press the MASTER button.
Thanks to Richard Beeson, we now have a copy of the Ensoniq SD-1 manual available for download.