Ensoniq EPS

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Ensoniq EPS Photo.jpg
Ensoniq EPS
Dates1988 - 1991
PriceApprox. US$ 2400
Technical specifications
Polyphony20 voices
Synthesis typeSampler
Aftertouch expressionYes
Velocity expressionYes
Keyboard61-note with polyphonic
Left-hand controlpitch-bend and modulation wheels
External controlMIDI

The EPS (Ensoniq Performance Sampler) was one of the first few affordable samplers on the market. It was manufactured from 1988 to 1991 by Ensoniq in Malvern, Pennsylvania, USA. The EPS was a 13 bit sampler and replaced the Mirage - widely regarded as the first truly affordable sampling keyboard.

The EPS had a straightforward interface that was easy to use, with configurable controls geared for live performance. Because it had two processors, it could load and play up to eight instruments simultaneously (with another eight on reserve). The display was a 22 character single line vacuum fluorescent display. It booted from an integrated floppy disk drive (sourced from Sony or Matsushita), or from a SCSI drive connected to the expansion bay. The EPS came with 256 Kwords of RAM on board. Ensoniq offered both a 2x (512Kword) Memory Expander and a 4x (1Mword) Memory Expander with SCSI interface. A company called Maartists offered both 4x and 8x memory expanders, allowing a total of 2Mwords RAM. Extra RAM allowed for longer and higher quality samples. The "2x" expander contained three 4x256Kbit and one 1x256Kbit chips, for a total of 13x256Kbits in addition to the onboard memory. The EPS was unusual in having a 13-bit sample memory wordlength, left-justified into the most significant bits of a 16-bit word.

The EPS used double-sided double-density 3.5" disks, formatted to 800k with ten 512-byte sectors per track. It could also read (but not write) Ensoniq Mirage sample disks.

The EPS uses MIDI and can be used as a controller of other instruments, or linked to a PC or Macintosh.

The EPS was eventually superseded by the EPS 16+ which upgraded the sample-size to 16-bits and added a 24-bit effects system. Other improvements included CD-ROM support in the optional SCSI interface and FlashBank storage for the OS and favourite sounds.

The EPS and EPS 16+ were both succeeded by the Ensoniq ASR-10 which was able to read EPS samples and disks.


Ensoniq EPS

The keyboard is of thick plastic construction of a dark gray color with 61 weighted keys. There are assignable pitch, modulation wheels, and two patch select buttons. The interior of the unit is accessed by removing four hex screws under the front of the keyboard and swinging open the rear-hinged control panel.

The whole unit was configurable through a custom operating system (latest version was 2.49 for the EPS and 1.30 for the EPS 16plus). After the system boots from the floppy drive, it flashes a "Tuning Keyboard - Hands Off" message while it calibrates its polyphonic after-touch keyboard. The 16plus was capable of storing the OS in the optional FlashBank, which removed the need for a bootdisk.

An optional Output Expander module allowed you to access eight discrete mono outputs on the machine, allowing you to separately mix levels and effects for each loaded sample.

The key limitations of the EPS were its proprietary disk format, and later a lack of support from Creative Technology, the current owner of Ensoniq. A 19" rack-mount version of both machines were also available in limited numbers.

Ensoniq EPS-16+

This model was superseded by the Ensoniq EPS-16+, released in 1991. The EPS-16+ was very similar to the EPS. Its main addition was integrated DSP effects and stereo audio routing. Due to the upgrade to 16-bit audio, the Output Expander on the 16plus was different, instead providing three pairs of stereo outputs, two from before the new effects chip.


The EPS is a performance sampler. Besides the main processor it contains a dedicated sound engine so that playing can be done whilst loading another sample. The main processor handles the I/O while the sound engine is responsible for keeping the audio running without interruption—this made the EPS especially useful for live performance situations.

The interface, although operating through a single line fluorescent display, offered rapid access to all functions by the intelligent way that functionality was broken into Modes and Pages.

Modes were: Load, Command, and Edit.

Pages were: Instrument, Sequence, MIDI, and System.

In addition to eight soft instrument buttons, it had a number pad (0-9), four cursor buttons, a value slider, and 'Yes' - 'No' buttons.

The vast majority of functionality could be accessed with less than three clicks: Mode - Page - Number Pad.

There was also a dedicated button for Sampling, and three for the built-in sequencer. The 16plus also had a dedicated button for configuring the effects DSP.

Easter Egg: There is a hidden menu in the Command-ENV1 page which contains Software Information, the names of the designers, a DC Offset Adjustment, and a keyboard calibration command.


Instrument pages would be prefixed by clicking a Mode (Load, Command, or Edit) -- yielding functions relating to loading, editing, and tweaking EPS sampled instruments. Instruments could contain a number of discrete samples which were patched into Layers - each with their own ADSR-like envelopes and keyboard ranges. A loop editor allowed you to define envelopes, cross-fades, and sample start-end, and loop points in real-time. It was possible to modulate the loop start with any source to give complex evolving sounds. On the EPS-16+ the Transwave loop mode allowed the start point to be modulated in exact "single-cycle" steps, giving effects similar to the PPG Wave. The Ensoniq manuals were famous for including quality tutorials for sampling and editing new sounds.


The Sequence pages allowed you to define sequences and songs. Simple quantization was available, and a crude, but effective step-editor to tweak individual sequence elements. Sequences (with up to eight instruments playing simultaneously) could be assembled into Song Steps. In assembling songs, you could define the number of repetitions of each sequence that comprised a song step. This made it relatively easy to score and arrange a song.

Sequences depended on having instruments being loaded into one of the eight instrument banks in the right order. Banks of instruments could be saved which could be loaded in by a song sequence so that loading the song loaded up all the appropriate sounds into the right places so everything would just play when you started the sequencer. In the 16plus, an effect was also assigned to a bank.


The EPS supports polyphonic-aftertouch on its 61 keys, and therefore allows a fair amount of expression as a MIDI controller. Sys-ex messages were supported over MIDI, and can transmit and receive on multiple MIDI channels simultaneously.


By using a dedicated sound engine in addition to the main processor, sound generation and disk I/O were handled separately. This allowed so-called load-while-play, a feature quite unique at the time. The user could boot the EPS and load some sounds while playing the ones that are already loaded. Then sample in a new sound, only to find that you're out of floppies to save your new sample to — the EPS OS will allow you to go ahead, format another floppy disk, and save your new sound without the system function getting in the way of playing the audio.

True to their very user-oriented approach, the EPS boot disk not only contained everything needed to run the sampler, but also a tiny operating system with the ability to create a bootable version of itself. This was an improvement on their earlier Mirage sampler, which required a special boot disk with a formatting program, and could not make copies of its own boot disks.

Further reading[edit]

  • "Retro: Ensoniq EPS16+". Future Music. No. 64. Future Publishing. December 1997. p. 47. ISSN 0967-0378. OCLC 1032779031.
  • "Ensoniq Performance Sampler". Sound On Sound. February 1988. pp. 36–40. ISSN 0951-6816. OCLC 925234032.
  • "Ensoniq EPS". Music Technology. Vol. 2 no. 12. October 1988. p. 50. ISSN 0957-6606. OCLC 24835173.
  • "Ensoniq EPS-M Sampler Module". Music Technology. May 1989. p. 14. ISSN 0957-6606. OCLC 483899345.
  • "Ensoniq EPSm". Sound On Sound. June 1989. pp. 70–71. ISSN 0951-6816. OCLC 925234032.

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