EMT 251 Digital Reverberator
A second-generation space machine that cost about as much as a house and put real, programmable acoustics on the console.
Overview
Ninety-five pounds, twenty-one inches by thirty-two and a half, and twenty thousand one hundred dollars. Those are the numbers a studio owner looked at in 1981 before signing for an EMT 251. This was not an impulse buy. It was capital equipment, priced and built like the console it sat beside. The 251 is the improved, second-generation successor to the EMT 250. It kept the "space machine" look of its predecessor, but by the manufacturer's own framing it was a quite different instrument inside.
The differences are the story. The 251 doubled the memory capacity of the 250, added internal error correction and self-diagnostic features, and sped up the processor to a 40 ns per-instruction cycle, down from 50 ns. Digital-to-analog conversion is 16-bit linear with 15 kHz bandwidth across all programs — a figure that, in the context of 1981, put the unit in rarefied company. The point of all that horsepower was denser, more refined reverberant images, and the company claimed unmatched dynamic and phase behavior as the payoff. A completely new control panel with an advanced dot-matrix liquid crystal display shows reverb curves, delay settings, and amplitude settings at a glance — a genuine departure from the knob-and-meter thinking of the era.
The 251 splits the difference between reverb and delay. It runs a reverberation program alongside three delay lines, each individually controlled, so the first, second, and third reflections can be placed by hand within a 0-120 ms window and assigned across the stereo output. A fourth delay line generates a reverberation cluster just ahead of the actual reverb onset, which smooths the transition into the reverberant field. Beyond the basic reverb mode the unit offers three special modes: delay, echo, and chorus. Delay mode gives up to four independently controlled delays as long as 440 ms each. Echo mode provides four loops - one primary and three ensuing - with loop length and feedback amplitude independently programmable. Chorus mode processes a single input into four independent outputs, each varying slightly in pitch and amplitude, and can separate any two chorus outputs by as much as 80 ms. Set short delays on those chorus outputs and stereo flanging becomes available on top of the chorusing. The delay and echo modes reach down below 4 ms, useful for broadening or fattening dry tracks without adding reverb at all.
The special reverb modes include Doppler-shift reverberation, non-linear decay, and extra-long reverb times. For post and broadcast work, the console-automation tie-in is the sleeper feature. The 251 is compatible with DC-type automation systems such as Harrison Autoset, and every function on the unit can be controlled that way. Reverb settings are recorded to a data track or disk alongside the fader information and decoded at mixdown to reproduce those settings precisely. That helped on a complex session cut across multiple passes. The manufacturer's own documentation gave the price and physical reality plainly: about 95 lbs and $20,100.
Some of what was said about the 251 at the time was marketing. Quad-Eight's System 5 advertising, which ran in Recording-Engineer (December 1980, p.41) and DB-Magazine (February 1981, p.23), positioned itself at less than half the price of an EMT 251 and only slightly more than a Lexicon 224, and claimed it sounded better than both. That is a competitor's sales copy, not an independent verdict. It shows how the 251 was priced against the field, not how it sounded. The period record does confirm staying power. Studio-Sound (June 1985, p.44) noted that the EMT 251 and 252 had been available for some time and that a recent update let both units be modified very simply, while Mix (May 1985, p.36) described the 251 as the improved second-generation version of the 250. Studios kept them in service for years. EQ later listed an EMT 251 among the outboard reverbs in both Bismeaux Studio in Austin and Sabella Recording Studios on Long Island, working alongside Lexicon PCM units and plate reverbs rather than replacing them.
For a collector, the 251 is a commitment. It is heavy, it is large, and it was never cheap. Its value today rests on the same things that justified the original price: the density of the algorithms, the reflection-placement control, and the automation integration that almost nothing else in its class offered. The internal error correction and self-diagnostics are cold comfort decades on, and prospective owners should expect the usual attention a machine of this age and complexity demands.
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