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The Kurzweil K250, manufactured by Kurzweil Music Systems, was the first electronic musical instrument which produced sound from sampled sounds compressed in ROM, faster than common mass storage such as a disk drive. Acoustic sounds from brass, percussion, string and woodwind instruments as well as sounds created using waveforms from oscillators were utilized. Designed for professional musicians, it was invented by Raymond Kurzweil, founder of Kurzweil Computer Products, Inc., Kurzweil Music Systems and Kurzweil Educational Systems with consultation from Stevie Wonder; Lyle Mays, an American jazz pianist; Alan R. Pearlman, founder of ARP Instruments Inc.; and Robert Moog, inventor of the Moog synthesizer.
In the mid-1970s, Raymond Kurzweil invented the first multi-font reading machine for the blind, consisting of the earliest CCD flat-bed scanner and text-to-speech synthesizer. In 1976, Stevie Wonder heard about the demonstration of this new machine on The Today Show, and later became the user of first production Kurzweil Reading Machine, beginning a long-term association between them.
In 1982 Stevie Wonder invited Raymond Kurzweil to his new studio in Los Angeles, and asked if "we could use the extraordinarily flexible computer control methods on the beautiful sounds of acoustic instruments?" In response, Raymond Kurzweil founded Kurzweil Music Systems, with Stevie Wonder as musical advisor. Kurzweil used the sampling technique that had been exploited in reading machines (such as the Kurzweil Reading Machine) and adapted it for music. Reading machines sample the characters in a text document to produce an image. The machines convert the light and dark areas of the image into text data stored in (RAM) and/or (EPROM), then output spoken text with a text-to-speech synthesizer.
Sound reproduction technique
The Kurzweil K250 utilizes a similar concept: Sounds are sampled, compressed & converted into digital data, stored in ROM and reproduced as sound via 12 separate DACs and analog envelopes (CEM 3335), which are programmed to simulate the dynamics and sustain of the original sound.. This method was called 'contoured modelling' by Kurzweil in marketing material and regarded as a proprietary scheme. Bob Moog, then a consultant at Kurzweil, was asked about the method in an article in Electronic Sound Maker in 1985:
About the 250: Kurzweil mentions something called "contoured sound modelling". Can you explain that a little? R.M: Yeah, it's a proprietary scheme... and 'proprietary' is a polite word for "we're not going to tell you what it is"! It is a very complex, elaborate software, a set of programs that are used to compress the data of a series of sounds, so that we can get it into a reasonable amount of memory. If we took just raw sounds and digitized them — every sound, every key on the piano is different, for instance. And within one key, every level of dynamics has a different waveform. It's just not that it's louder, the whole waveform changes.
Which is a much more natural sound. R.M: Yeah, now we want to get all that information in there, we want to be able to construct those differences, but we want to eliminate all the superfluous information, you know, the redundancy, the information that we don't need in order to reconstruct this. And that's what "contoured sound modelling" is all about. If all the sounds that are in the machine now were without the data being compressed, it would take more memory chips than are made in a year!
This method greatly reduced the number of then-expensive EPROMS needed whilst maintaining the dynamics of the sound which would be otherwise compromised by compression. The CEM 3335 integrated voltage controlled amplifier  provided exponential gain to reconstruct the dynamics that were lost in the compression.
A prototype of the Kurzweil K250 was manufactured for Stevie Wonder in 1983. It featured Braille buttons along with sliders (potentiometers) for various controls and functions, an extensive choice of acoustic and synthesized sounds, a sampler to record sounds onto RAM and a music sequencer with battery-backed RAM for composition. During production of the Kurzweil K250 at least five units were manufactured for Stevie Wonder.
The Kurzweil K250 was unveiled during the 1984 Summer NAMM music industry trade show. The Kurzweil K250 was manufactured until 1990, initially as an 88-key fully weighted keyboard or as an expander unit without keys called the Kurzweil K250 XP. A few years later a rack mount version called the Kurzweil K250RMX also became available.
The Kurzweil K250 was the first electronic instrument to faithfully reproduce the sounds of an acoustic grand piano. It could play up to 12 notes simultaneously (known as 12-note polyphony) by utilizing individual sounds as well as layered sounds (playing multiple sounds on the same note simultaneously, also known as being multitimbral). Until then the majority of electronic keyboards utilized synthesized sounds and emulated acoustical instrument sounds created in other electronic instruments using various waveforms produced by oscillators, and prior to that there were instruments such as the mellotron and orchestron which used tape loops. Five other manufactured digital sampled sound musical instruments were available at that time: E-mu Corporation's E-mu Emulator and E-mu Emulator II; Fairlight Corporation's Fairlight CMI; and New England Digital's Synclavier I and Synclavier II.
- "All I Ask of You" – from: Phantom of the Opera composed by: Andrew Lloyd Webber – performed by Christopher McGilton and Nancy Smith using the Kurzweil 250 solely as the accompaniment 
- "Gesù bambino" composed by: Pietro A. Yon – performed by Christopher McGilton and Nancy Smith using the Kurzweil 250 solely as the accompaniment 
- Christopher Yavelow – Countdown (For the Nuclear Age) – The Worlds First Computer Opera, completely synchronized from the baton of the conductor to the Kurzweil K250 
- Christopher McGilton – Religious/Sacred Music in .mp3 format performed on the Kurzweil 250 and Yamaha MU-50/80 Sound Module  or 
- Craig D. Tollis – The Happy Frog: Kurzweil K250 – Two demo recordings of the Kurzweil 250 
- Jane Brockman – Kurzweil Etudes: original compositions performed on the Kurzweil 250, listen to 3 excerpts from the Opus One recording:
- Pamela J. Marshall – Spindrift Recordings – Noises, Sounds & Strange Airs, "Child's Play"
- Pauline Oliveros – Dear. John: A Canon on the Name of Cage 
- Steven Johannessen – K250 Demo Music Showcase at the Middle Of Nowhere 
- The Kurzweil 250 Rock Block – Play the 45 RPM Kurzweil 250 Demo Record virtually! 
- The Kurzweil Rocks! – Play the 45 RPM Kurzweil 250 Demo Record virtually!
- The Virtual Kurzweil 250 Sound Sheet – Play the 45 RPM Kurzweil 250 Demo Record virtually!
- Philipp Koltsov – Russian composer & pianist plays Kurzweil 250's patch #1 Grandpiano Demo 
Audio and video
- ASJ Avantius – Muzika u domaćoj kinematografiji ( II DEO ) 
- Bach's Nightmare: The Ultimate Rape, or The Art of Kitsch 
- CBS News Interview with Joel Spiegelman in September, 1988 on New Age Bach and the Kurzweil 250 
- Chick Corea Electrik Band – "The Dragon" (Note the Kurzweil 250 is to Chick's left on the bottom and string sounds are played on it during the performance) 
- Christopher McGilton – "Magnificat" performed on the Kurzweil 250 and Yamaha MU-80 Sound Module – 
- Christopher McGilton – "No Greater Love" performed on the Kurzweil 250 and Yamaha MU-80 Sound Module – 
- Clinton S. Clark – Film Scoring Portfolio 
- FX – Kevin Loch at Lisner Auditorium Nov. 8, 1986 
- Joel Spiegelman Interview on the Joe Franklin Show, August 1988 
- Keith Emerson – Emerson, Lake and Powell with Paul Shaffer and the CBS Orchestra on the Late Show with David Letterman (Note that two Kurzweil K250's are being played live – one by Keith Emerson and the other by Paul Shaffer) 
- Kurzweil – It all started with Ray Kurzweil – The story of Stevie Wonder's technical challenge to Ray Kurzweil that ultimately motivates the inception of Kurzweil Music Systems. 
- Kurzweil 250 Demo Cassette (Jazz / Orchestral demo from a great sampler-synth) 
- Kurzweil 250 Demo Cassette (with voiceover explaining history and features) 
- Kurzweil 250 Rock Block Demo 33 1/3 RPM Record 
- Mutabaruka – "The Mystery Unfolds" 
- Pat Metheny Group – "Daulton Lee" (information in Italian) 
- Ray Kurzweil – Ray Kurzweil Appearing on Worldnet – Demonstration of the Kurzweil 250 
- Robert Estrin – Piano Questions: A Great Digital Piano – The Kurzweil K250 
- Santino Famulari – "La Campanella" on a Kurzweil 250 – 
- Steven Johannessen – Visual Music Showcase at the Middle Of Nowhere 
- The Big Cruise – "Don Lampasone" (ASCAP) 
- The Mosquito 
- Wayne Shorter Quartet – "The Last Silk Hat" (North Sea Jazz 1986) 
- Sound on Sound – Size Does Matter Kurzweil K250 Workstation Keyboard (Retro) 
- Sound on Sound – Synth Secrets 
- The Age of Spiritual Machines  or 
- The Man and the Machine:An Interview With Ray Kurzweil 
- Time Magazine – Can We Talk? An article about Speech-to-Text recognition and about the Kurzweil 250 
- Virtual Organ – Virtual Instruments:Joe Barron, Present at the 1984 NAMM Show when the Kurzweil 250 was introduced: 
- What's New In Electronic Music; The Art Advances At Warp Drive: A. Arnold Anderson, New York Times 
- Synthony's Synth & MIDI Museum 
- Mastering the Kurzweil 250, Volume One: User's Guide and Volume Two: Reference Manual, Copyright 1988 Kurzweil Music Systems, Inc. 
- Synrise – Brief information on the Kurzweil 250 (In German) 
- Byrd, Donald, & Yavelow, Christopher (1986). The Kurzweil 250 Digital Synthesizer. Computer Music Journal 10, no. 1, pp. 64–86.
- "A Biography of Ray Kurzweil". Kurzweil Technologies, Inc. 2008.
- The Age of Spiritual Machines (Viking, 1999)
- CEM 3335 datasheet