First produced in 1979, the Korg* Lambda ES50 was a monumental wedge of polished wood and analogue electronics designed to take the string synth concept to a higher level. It distinguished itself from string synths that had gone before on a number of fronts: it was fully polyphonic, not paraphonic; it had a host of real-time tonal and envelope controls over the sound; it combined string and ensemble sounds with key sounds like pianos, EPs and clav; and most of all, it included a rich, analogue, swirling, stereo
This fact alone set it head and shoulders above its contemporaries. The Lambda's stereo chorus (which it calls "Chorus Phase") makes for a superbly lush, expansive sound, thickening the strings and other orchestral patches, filling out the soundstage, and warming a whole mix with a single button-press. It's a little touch of analogue magic!
The tones are a great selection of sounds. The Lambda divides its tones into Percussive (for which read "keyboard") and Ensemble (for which read "orchestral). On the Percussive side of the panel we get a great EP, a nice sharp Clav sound, a thick and funky Piano, and a very useful high-pitched Harmonics sound that combines well with the other sounds. There's also a Key Click control for the EP hidden away, to give its attack more bite. On the Ensemble pane we have Brass, Organ (as in church organ), Chorus (a wonderful, delicately smooth Vox Humana-type sound), and twin String tabs set an octave apart. These can all be combined freely to get some really complex tones going.
The Lambda also incorporated twin detunable oscillators for some of its tone production, which allows a second, distinct way of fattening and thickening a sound. Naturally, the detune and the "ensemble" chorus can be selected simultaneously. This is pretty cool. Add in an entirely separate resonant filter responsible for giving the Brass patch its characteristic attack "wow", a Tremolo control for the keyboard-style sounds, and a Vibrato control, and you've got a surprising number of tone-sculpting tools built right in. The Lambda is a machine that bridges the gap between preset string synths on the one hand and programmable analogue polysynths on the other: it lacks the full control of a polysynth, but goes far beyond what string synths had considered necessary. The result is a hugely usable keyboard which spans a wide tonal territory: thin to thick, sweet to rich, percussive to smooth.