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A late-1980s synth from Kawai; the first of their two attempts to commercialize additive synthesis. The K5 is a digital synth, built around two harmonic generators. Each generator was capable of producing a fundamental and the 2nd through 63rd harmonics for that fundamental. The two generators could have their fundamentals tuned to a desired interval, or they could be configured in a single-tone mode in which the second generator provided 63 additional harmonics for the first generator, extending the single tone to 126 harmonics.

The level of each harmonic could be set individually. A set of four multi-segment envelope generators was available for the harmonic generators; each individual harmonic could be assigned to have its level controlled by one of the four envelopes, or be set to a static level. Assigning different groups of harmonics to different envelopes allowed the timbre of a sound to be varied considerably over time. A digital "amplifier" controlled the overall output level of a note, with its own six-segment envelope generator. There was also a digital equivalent of a VCF; however, it was only a single-pole design lacking resonance, and most performers found it not very useful.

The user interface proved to be a challenge due to the very large number of parameters associated with the harmonic generators, and was somewhat limited by the display technology available at the time. The K5 contains an early version of a large, monochrome LCD display which displays parameters on a number of pages, selected by page buttons on the panel. Notable are the pages which set the harmonic levels for the harmonic generators; due to the limited display resolution these are necessarily cryptic (some on-off parameters are represented by single pixels), but once learned they are quite efficient to use. User input is of the one-knob style (like most synths of its era); cursor buttons select a parameter to be edited via a single large rotary encoder. The harmonic editing display pages contained some "macro" capabilities to somewhat speed up the editing of harmonic levels. The user could select a block of harmonics whose levels could be increased or decreased simultaneously; it was also possible to edit only the odd-numbered or even-numbered harmonics within a block.

Patch memory consisted of 48 writeable patch locations, and 48 "multi" setups to be used with the multitimbral mode. The synth had 16 voices, and a voice allocation page allowed the user to assign a fixed number of voices to one or more MIDI channels if desired. There were four assignable outputs and a "mix" output. The mix output was rather noisy and suffered from low output level; modifications are published on various Web sites to fix this, but due to the noise level in the mix output, many performers prefer to create a multi setup and assign a patch to it even when playing monotimbrally, so that the audio can be routed to one of the quieter assignable outs. The K5 was made in two configurations, a keyboard version with a five-octave span, and a keyboardless version whose enclosure was shaped so that it could either be rack mounted or used as a tabletop unit. External control for both version was via MIDI.

Kawai has released no information on how many K5s were built; it was not a popular synth. Despite this, it is moderately priced on the collector market because many performers struggle with or don't want to put in the effort to learn additive synthesis. However, the synth remains popular with a subculture that has taken on the task of mastering additive synthesis, or just ;looks for something different. Nearly all existing units need the LCD backlight replaced if it hasn't been done already.