Eventide Model 1745M Digital Delay
Eventide's memory-based delay line. It swapped shift registers for RAM and gave studios flanging, doubling, and pitch change in one chassis.
Overview
The "M" in 1745M stands for memory. Earlier digital delays used shift registers to hold the signal. Eventide's Model 1745M used Random Access Memory integrated circuits for delayed signal storage instead. That gave the unit a large number of delay taps and the audible illusion of continuously variable delay. It also meant delay switching could be done without transients, so settings could be changed during soft passages without a bump. For a studio tool of its day, that was a real practical advantage.
Eventide's own advertising billed the 1745M as a complete delay package: flanging, tunneling, pitch changing, reverb, recirculation, and comb filtering all in one lightweight chassis. The pitch change card was optional. The company also offered plug-in modules, including a wide-range pitch-changer/tempo regulator with drive electronics for Ampex, MCI, and 60Hz machines.
By the early 1980s, Eventide's published model list gave the 1745M a delay time of 0 to 320ms, continuously variable. That fits the "continuously variable delay" claim the company made from the start. Dynamic range was quoted as greater than 90 dB. The CMOS circuitry cut power consumption sharply, which in turn reduced the unit's ventilation requirements. Signal level indication was more versatile than on earlier designs.
The 1745M was designed with automation in mind from the outset. When Eventide introduced a microprocessor-controlled remote control card, the company noted that even early units already in service for up to two years would need only minor modifications to accept it. The card used the ANSI/IEEE 488/1975 standard interface bus, so it worked with computers including Hewlett-Packard machines and the low-cost Commodore PET. It allowed remote setting of delay and control of the "repeat" and "double" modes. It added two features: automatic flanging with digital-delay quality, and a vocal or instrumental doubling effect in which the delay was varied in a pseudo-random manner. That was Eventide's answer to the "mechanical" sound of note-for-note doubling on conventional delay units. The remote itself cost $550 or £300.
The 1745M was promoted heavily in the British studio press of the late 1970s. Studio Sound (February 1978, p.61) ran the company's copy describing the system as offering "unequalled versatility and portability" combined with studio-quality specs, with the pitch-change card listed as optional. The same magazine (March 1978, p.18) repeated the pitch-change-card-optional framing. The unit also appeared in Eventide's AES convention previews. Studio Sound (May 1978, p.70) listed the 1745M among the gear on show alongside the H910 Harmonizer, the 2830 Omnipressor, and the FL201 Instant Flanger.
The 1745M's memory-based architecture was debated in the trades. A period commentary on digital versus analog delay design argued that centralizing real-time control and computation signals in a common data bus and processor, the approach Eventide took, carried trade-offs. One was the risk that a single component failure could take down the whole system. Another was the difficulty of shielding low-level audio circuitry from the radiation of high-speed digital lines.
A complete 1745M set is a different proposition from the delay unit alone. The automation remote is a separate item, priced at $550/£300 when new. The CMOS design and modest ventilation needs are points in its favor for long-term serviceability. The optional pitch-change and tempo-regulator modules are the parts most likely to be missing from a used example. Eventide's own literature never claimed the 1745M was a reverb in the modern sense. It was a delay system first, with reverb among its tricks.
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