Kurzweil K150 (1986)
A rack-mount piano module that turned out to be far stranger and more capable than its factory presets let on.
Overview
The K150 is a quad-height rack enclosure, seven inches tall and roughly fifteen and a quarter inches deep. The front panel has double data-entry keypads, a large alphanumeric LED display, a volume control and a stereo headphone jack. Around back there's an unbalanced line-level output, a footswitch input, cassette in and out, MIDI In/Out/Thru, and a rear-mounted cooling fan. Electronic Musician (1986) reviewed it at a list price of $2,995. The review called it Kurzweil's long-awaited rack-mount spinoff of the original K250 keyboard - a 16-oscillator, multi-timbral digital sound module with a comprehensive MIDI implementation.
First thing to get straight: the K150 is not a sampler. Sounds live in ROM and are replayed, not recorded. It ships with 14 resident voices - three acoustic pianos, two electric pianos, two harpsichords, acoustic bass, two electric basses, vibes, marimba, and jazz and rock organs. It also has an eight-voice Sound Block with three guitars, four synth sounds, and congas. You play it from a remote MIDI controller, which is not provided.
The acoustic piano is the headline, and Electronic Musician (1986) was unusually taken with it. The review called the sound incredibly accurate and very close to the K250's acoustic piano timbre, including a simulation of the sympathetic vibration of the undamped treble strings. It also noted the voice-assignment routine is forgiving of long arpeggios with the sustain pedal down, often sounding as though more than 16 oscillators were available. The flip side: repeated strikes with the pedal down can truncate the envelope decay as oscillators get reassigned, and notes occasionally ring out uncontrollably loud or bright with an overlong decay. The review concluded the piano voice depends heavily on the player's technique and grasp of the unit's limitations, plus the amplification and EQ in use.
Beyond the piano, the quality is uneven and the review said so plainly. Acoustic bass and nylon-string guitar are very good, vibes and marimba are noteworthy, and the Rhodes voice is excellent. Most of the organ and synth voices are more pedestrian. The Kurzweil string sounds are conspicuously absent. Electronic Musician (1986) reported that programmer Pam Marshall attributed this to the K150 voices using an additive synthesis process rather than the sampling techniques of the K250, with ensemble voices not yet developed for the K150. Other Sound Blocks were reportedly in the works, including a trap set to go with those congas.
The architecture underneath is where the K150 gets interesting. Voices combine with control parameters to form layers. Each layer has independent control over tuning, transposition, chorus enable, vibrato enable, EQ enable, and Timbre Shift. Timbre Shift replaces the spectrum of a given note with that of a higher or lower note. It's analogous to a sample transposed above or below its range, but without the pitch shift. It can be fixed or driven by MIDI attack velocity or an assignable controller. Per the same review, it is also the only timbral-control method on offer: no amplitude envelopes, no VCFs, nothing of the sort. Layers combine into regions, which are keyboard zones, and voice, layer, and region parameters together are stored as programs. The unit holds up to 256 programs and ships with 76 presets that can be overwritten or recalled at any time, a decision the reviewer specifically praised.
The global processing is more capable than the "another rack-mount piano" reputation suggests. The chorus stacks up to seven voices on a given key, with programmable delay, detune, and amplitude decay per successive voice. That makes it essentially a MIDI delay unit. It can range from flanging and echo to octave doubling and chromatic glissandi, with depth fixed or controlled by mod wheel or aftertouch. The voice-assignment routine will temporarily steal chorus-assigned voices when more polyphony is needed. Vibrato offers rate, depth, and delay, with triangle and square waves plus full control of waveform phase, offset, and symmetry, and arbitrary ramp and pulse waves can be produced. Parameters are global, but the K150 responds to polyphonic aftertouch, so different vibrato amounts can be applied per key from a suitable controller. The equalizer digitally simulates an 8-band graphic EQ with centers at 62.5, 125, 250, and 500 Hz and 1, 2, 4, and 8 kHz, up to 12 dB of boost and 30 dB of cut per band. The 62.5 Hz and 8 kHz bands shelve and the rest peak.
Multi-timbral operation is full. In Multi mode each MIDI channel can be assigned a different program, and as many as 16 monophonic lines (one per oscillator) or various mono/poly combinations can play at once, each with its own timbre, bounded by the 16-oscillator ceiling. Programs using more than one oscillator per note reduce available polyphony, but dynamic voice allocation keeps temporarily inactive channels from wasting voices. Mapping functions handle program-change access and can even set alternate intonation such as Just or Mean Tone tuning. Poly aftertouch can be mapped to polyphonic touch-sensitive pitch bend, and a keyboard velocity map adjusts response curves to match various controllers. The review warned that several controllers tested were not compatible with the pre-programmed curves, so expect to spend time tweaking that function.
A planned optional update called Sound Lab was to let users create voices via additive synthesis routines on a personal computer and download them to the K150 over MIDI. The reviewer, judging the factory sounds, expected it to be tremendous. A separate Sound Modeling program for the K150FS synthesizer, using an Apple IIe, was announced in Recording-Engineer (July 1987, p.80). It allowed design of frequency and amplitude envelopes for up to 64 partials per sound model in data table or graphic display, and required Version 1.6 software. The Electronic Musician (1986) review also noted the K150 can theoretically load and save programs via cassette or MIDI, but those features were not implemented on the review unit. The owner's manual is thorough but poorly indexed, and the review copy lacked voice and program listings.
Given the factory programs, the period press said the K150 is likely to be viewed as another rack-mount piano. The review called that an unfortunate oversimplification, since its multi-timbral capability and promised additive synthesis set it apart, and even judged purely as a piano module its performance is commensurate with its price. A 16-oscillator sound module can't replace a piano in many jazz and classical contexts, but the review still called it a pretty amazing piece of hardware. Sound-on-Sound (December 1998, p.275) listed a used K150 Sound Module at £599 in its ex-demo/secondhand pages.
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