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History of Delay

Delay is an invaluable effect which can be used to enhance a mix, create a fuller, more dimensional sound and even allow ‘looping’ where solos can be played over backing chords or arpeggios. During the twentieth century several different means have been utilised to create the delay effect. This article briefly outlines the history and development of electronic signal delay technology.

Line Delay

telegraph_wire_delay_line2 — The first electronic delays were created by sending signals along telephone wires.

Before the invention of magnetic recording the first artificial time delays were created by utilising telephone lines as the storage medium. A radio station would transmit their signal out over a phone line to a city many hundreds of miles away on the other side of the country and then back again. The time taken for the signal to complete the outward and return journey back along the phone line would be the length of delay. Now, the propagation velocity of an electrical signal in a copper wire conductor is incredibly fast—close to the speed of light—a velocity of approximately 300 million meters per second. This meant the line had to be physically very long in order to delay an input signal just a few milliseconds. When the signal returned it would then be mixed with the original signal with the aim of enhancing the quality of radio broadcasts. This form of delay was not very practical because the delay time was fixed and also depended on the infrastructure of the telephone company to work.

Magnetic Tape Delay

With the development of magnetic tape recording in the late 1920s there came new possibilities in delay technology. Magnetic recording works according to the following principle. The tape runs at a constant speed. The writing head magnetises the tape with current proportional to the signal. The result is a pattern of magnetisation is stored along the length magnetic tape, that can be played back later to reproduce the original signal. With the ability to record a sound and play it back came the tape delay.

philips_el3503_reel_to_reel_tape_machine — Philips EL-3503 tape machine. The BBC Radiophonics Workshop used 3 of these professional machines to create delay and looping effects.

Tape delay units were large, yet (trans)portable tape recorders that incorporated a recording head and a playback head. While the guitar player is playing the original signal is recorded by the recording head and then it passes through the playback head milliseconds later creating the delay effect. The length of delay depended on the distance the tape had to traverse between the playback head the recording head.

This technique was utilised in the mid 1950s to create the “slapback” echo effect that defined the rockabilly sound and many early rock & roll recordings. To create slapback the delay is set for a repeat rate of about 150 to 200ms with just one repeat at almost the same amplitude as the original signal. A good example of this can be heard on Scotty Moore’s guitar-work on “That’s All Right” by Elvis Presley. The sound engineer at the time, Sam Phillips was to use this effect on many recordings and it became a trademark sound of Sun records.

At this time there were several innovators developing portable delay units based on magnetic tape technology, notably Charlie Watkins (inventor of the Copicat) and Ray Butts (Maestro ‘Echoplex’). Now delay could be used in live sound applications. As these units developed over time they started adding more playback heads and tape speed controls giving delay more flexibility than it had ever seen before. With the addition of more tape playback heads delay could now feature more repetitions (multi-tap) of the same signal instead of just one. The addition of speed control or movable playback heads allowed for the first time the flexibility to change the delay speed on-the-fly. Many of these units are still used today in recording studios and sometimes in a live situation although this is rare.

This section would not be complete without mentioning the Binson Echorec, which was considered the top of the range echo unit for its time. Binson, Milan, Italy developed a storage medium based on a steel/alloy disc or drum, which carried a durable flat metal band around its circumference. This offered a significant improvement in terms of stability over tape delay. The Echorec was utilised by many artists, such as David Gilmour to create spacious and ambient sounds which literally defined the Pink Floyd sound during the 1970s.

Oil-Can Delay

fender_echoverb — Fender Echoverb III oil-can delay

During the 50s and 60s magnetic tape was the dominant method for creating delay effects, however there is another, esoteric technology, known as oil-can delay, invented by Ray Lubow (Tel-Ray). Instead of magnetic tape, these units house what appears to be a tuna can filled with oil which works as a dielectric, i.e. it can store a charge or signal. A motor drives a rubber belt to spin a flywheel fitted with a pickup inside the can. The oil stores signals electrostatically (rather than electromagnetically, as with a tape) and the pickup functions as the recording head, sloshing around in the oil to produce echo. The imperfections of this transport mechanism gave oil-can delay a unique sound that is a blend of reverb and warbling vibrato.

Several companies marketed these devices under various names. Fender sold the Variable Delay, the Echo-Reverb I, II, and III. Gibson sold the GA-4RE from 1965-7. Ray Lubow himself sold many different versions under the Tel-Ray/Morley brand, starting out in the early sixties with the Ad-n-echo, and eventually producing the Echo-ver-brato and an electrostatic delay Line. You can hear the effect on many of Ry Cooder’s recordings made in the late 50s.

Solid-State Delay

In 1969 F. Sangster and K. Teer of the Philips Research Labs invented the Bucket-Brigade Device (BBD). This device operates as delay by transferring charge packets from one transistor/capacitor cell to another. The signal would be split in two upon entering the analogue delay unit so that half the signal was routed directly to the output while the other half would pass through the BBD. This delayed signal was then mixed with direct signal. Because the signal had been slowed down as it went through the series of capacitors it would reach the output phase just a little behind the point that the two signals had been split, thus creating a delayed repetition of the original signal. BBD technology is almost universally (and incorrectly) referred to as being analogue, but strictly speaking it is hybrid digital/analogue since the signal is sampled in the time domain.

mn3001_bbd_delay_chip — Panasonic MN3001 512-stage bucket brigade delay IC

By the mid 1970s several manufacturers had compact BBD delay pedals on the market. These pedals suffered from severe high frequency loss (-3dB point at 3KHz) because some pretty steep low-pass filtering was required to remove clock noise. There was also noise degradation when the devices were pushed to create longer delay times, so their delay time was typically limited to around 300ms. These shortcomings were eradicated by the new digital delay lines that was becoming available, however the digital technology was so expensive at the time that many studios and musicians continued using BBD delays. Ultimately, the development of cheap, mass-manufactured digital delay technology with increased features greater flexibility, longer delay times, packaged in a small stomp box format made digital the dominant delay for the consumer market.

The Future

Well, it has to be a retro-future. As an analogue purist, I’ve yet to be inspired by the intrinsic tonal qualities of BBD or digital technology, which lack the magic of magnetic tape or drum echo/delay units—especially the vintage ones that require a great deal of care and maintenance. It seems to me something is lost when a signal is digitised and I’m not entirely convinced engineers have been able to fully explain or scientifically quantify what it is about the sound of tube/analogue systems that makes them so involving and subjectively pleasant to listen to. These audio technologies are physically and operationally very different animals, however it could be that the greater human involvement needed to understand and work with the idiosyncrasies of early and temperamental tape delays also plays some, vital role in the creative process. This human involvement is lost when the technology becomes more accessible and easier to use—like those paint by numbers pictures. It’s fascinating to ponder and philosophise on this, but on a more pragmatic note, I look forward to engaging in further research and tone exploration, to develop Effectrode’s own unique all-tube delay line…

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History of Delay