It might come as surprise, but digital delay units had been used in recording studios for automatic double tracking (ADT) years before the first BBD units were even on the drawing board. Eventide Clock Work‘s DDL 1745 hit the music scene in 1971. At this time Eventide were a real melting pot of creativity, exploiting state-of-the-art computer hardware—RAM (Random Access Memory), ADCs (Analogue-to-Digital Converters), DACs (Digital-to-Analogue Converters), shift-registers, glue logic, crystals and suchlike)—to create innovative new audio products for the recording industry.
“If audio could be digitized with high enough fidelity, it could be stored as digital bits, converted back to analog and, voila, you would have achieved delay – in real time, with no moving parts. By 1970, the bits and pieces became available to build a commercial product.” — Tony Agnello
From day one the audio quality of digital delay left BBD in the dust. Its frequency response was wider, distortion was lower, its noise floor was lower and dynamic range wider and it had untapped potential—it ultimately went on to perform all kinds of astounding signal processing magic; freezing, reversing, pitch-shifting and harmonizing with no signal degradation. But, in 1970, there was just one small drawback: digital hardware was very, very, very expensive—the DDL 1745 retailed for a wallet-melting $28,000-00 in adjusted dollars.
The stratospheric cost of digital delay units could only be justified because the studio time required to set up reel-to-reel tape machines and use them creatively for ADT effects was vastly time consuming and even more expensive. The same could not be said for the guitar effects industry, however. Such a huge price tag was way beyond the budget of most musicians who wanted to create slapback echo and delay effects. The prohibitive cost is in part why it took the best part of a decade for the first digital delay pedals, such as the Boss DD-2, to appear.
Additionally, digital circuitry required a substantial amount of power hungry electronic hardware to do the job. This discrete hardware ran hot. Not only that, early 1970s delay units, such as Lexicon’s ‘Delta T-101’ and Pulse Audio’s ‘Model One’, were big, bulky rack-mounted appliances 2U or 3U, even 4U high. Eventually, the development of cheap, more compact DSP (Digital Signal Processing) chip sets with increased features, greater flexibility and longer delay times made the stomp box delay as we know it possible; and digital delay became ubiquitous.
How Digital Delays Work
Early computers such as UNIVAC utilised mercury delay lines as memory. The principle of operation is analogous to digital shift register and BBD chips, however the memory storage medium is a tube filled with mercury. At one end of the tube, a transducer converts an electrical signal into sound. The sound then propagates through the mercury to the other end, where a second transducer converts it back into electricity. This electrical signal is fed back to the input of the delay line, and while a closed feedback loop is maintained, the delay line “remembers” the information. UNIVAC’s mercury delay lines each contained 20Kg of liquid mercury, maintained at a temperature of 40°C—the shift-register chips and BBD utilised in delay effects units are somewhat more compact and safer!
“A delay-line memory resembles the human device of repeating a telephone number to one’s self from the time it is found in the directory until it has been dialed.” — Fundamental Principles of Switching Circuits and Systems by AT&T Bell Telephone Laboratories, 1961.
Digital delay is not perfect though. Like BBD chips and magnetic tape, it has it’s shortcomings. These shortcomings come with strange and obscure names like quantisation, jitter, non-linearity, non-monotonicity, aliasing, folding, missing codes, gain and offset errors. Terms that are meaningless to the laymen, even some electronic engineers. What do they mean? Well, in practice they manifest themselves as nasty, unpleasant sonic ‘artifacts’; unnatural and unmusical distortion or signal mangling that does no favours to the tone of an electric guitar.
Although horrible for guitar, these artifacts do find good use for industrial and harsh, abrasive special effects in dance music, and for creating cool ambiences for dystopian, cyberpunk, sci-fi movies. Over time, effects designers have (almost) engineered these artifacts out of existence, either by increasing sampling rates and bit resolution or using compansion and pre-emphasis/de-emphasis techniques, finally allowing the crystalline and perfectly pure sound digital to shine through. Well, mostly. Despite the technical perfection of digital, guitarists still niggle: they found this purity to be boring, and uninspiring. To create music, they needed their effects to be musical, not to be mathematically perfect. They desired “grit”, “texture”, “complexity”, even for the sound to be sleazy and cheap; in short, the kind of sounds they were getting from those tired old tape echos.
The counter revolution had begun: Analogue effects became ever more highly sought after and crazily expensive; the ‘Echoplex’ [‘Tube Tape Echo‘ by Mike Fuller] and ‘Echomatic‘ [Eric Snowball] tape delays were resurrected; effects manufacturers woke up to the fact that musicians found the artifacts of analogue technology creatively inspiring (and therefore desirable) and recomputed their trajectory, setting their sights on replicating (modelling) the sound of analogue gear by adding noise, wow & flutter and limiting the frequency response.
Some of these digital effects, such as Pete Celi’s (Strymon), DSP (Digital Signal Processing) chip based pedal, the ‘El Capistan’ tape delay, and Sean Costello’s Valhalla delay and reverb VST plugins added a unique, hi-tech twist to the sound of vintage delay. These digital emulations didn’t sound exactly like the real thing, because a model or simulation, at best, is only an engineer’s best guess as to what some vintage piece of audio equipment sounds like; and built from digital technology, which, like all technologies, has its flaws and limitations. These things didn’t really matter though, because the new wave of digital effects added texture, complexity and character, and more importantly, inspired musical creativity, which, in the end, is what it’s all about.
And just one final thought: The sleek, new, modern delay units of today are physically and operationally very different animals to the old, dirty, temperamental delays of the 1950s and 60s. They don’t just sound different, they’re physically different, and so the experience of using them is different too. Greater human involvement is needed to deal with the idiosyncrasies of, say a vintage ‘Echorec‘ machine. I’m convinced this plays a vital role in the creative process. This human involvement is lost when the technology becomes more accessible and easier to use—like painting a picture by numbers, where the end result might be excellent, but it’s also very predictable. Without struggle there is no progress. But, perhaps that’s a conversation best left for another day; we’ve reached the end of the line: we’ve arrived back in the present.