Lexicon Model 91
A 120-millisecond digital delay that Lexicon pitched at churches and school auditoriums. ABC quietly used it to keep the evening news in lip sync.
Overview
Lexicon's ad copy for the Model 91 listed "churches, schools and colleges, community auditoriums and similar installations." That usually means look elsewhere. Here it doesn't. Lexicon billed the Model 91 as the little sibling of the Model 102, the company's "sophisticated big-system" PCM delay. It has the same converter technology and the same Delta-T delay architecture, in a package for budgets that couldn't reach the 102. Modern Recording (October 1979, p.103) ran that pitch, and the copy is candid about what was cut and what wasn't. The budget was the target. The engineering was not.
The numbers back that up. The Model 91 delivers 0 to 120ms of delay, adjustable in 7.5ms increments. That step size matters, because a delay line you can only nudge in coarse steps is hard to dial in for tight doubling or precise pre-delay. Lexicon quotes dynamic range greater than 90dB and noise and distortion below 0.08%, and says plainly that it got there without delta modulation. In the late '70s, plenty of budget digital delays hit their price targets by accepting the artifacts of delta-mod conversion. Lexicon is saying it didn't.
The front panel has a 5-level LED headroom indicator, which beats setting levels on a delay with no metering at all. There's also an automatic audio bypass that engages at zero delay or in the event of a fault. That's the kind of fail-safe a broadcast or installation user notices only when it saves them. The whole unit is modular, built for "fast, easy, on-the-spot maintenance."
The units ended up somewhere unexpected. The Model 91's public identity was small-budget install work, but ABC Television's broadcast engineering group evaluated several units before the 1980 political conventions and chose the Lexicon. They used it at both conventions and on coverage of President Reagan's 1981 inauguration. The network also leaned on it to hold lip sync for World News Tonight, particularly when anchors were spread across Washington, Chicago, and London under central control in New York. The catch, documented in a broadcast-engineering account of the period, is that the Model 91 required an operator to dial delay offsets in by hand. Getting correct lip sync took real skill and no small amount of guesswork. ABC eventually asked Lexicon to build an enhanced model that could detect frame offset automatically. That request produced the Model 1300, delivered in July 1983.
The Model 91 is a single-channel delay. Its sibling, the Model 92, is the same machine with two delay outputs instead of one, and Lexicon positioned the 92 for studios needing delay for doubling or echo pre-delay. The Prime Time Model 93 went further, with two independently adjustable outputs, mixing for delay and reverb, an integral VCO for vibrato, doppler shift and flanging, and long-delay effects up to 2 seconds. The 91 sits at the bottom of that ladder: one output, 120ms, and the same 90dB-plus, sub-0.08% performance Lexicon claimed across the line.
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