One of the most innovative devices at Abbey Road was the EMI RS56, a powerful outboard equaliser more commonly known as the UTC, short for “Universal Tone Control.” Originally developed for disc cutting, engineers were granted special permission to use the UTC during Beatles tracking and mixing sessions only.
The EMI RS56 was created in 1951 by EMI Technical Engineer Mike Bachelor, designed as a “quickly adjustable and versatile equaliser.” Functionally, it was a form of semi-parametric EQ, offering a degree of flexibility that predated commercial parametrics by decades. Its controls were stepped, not continuously variable, which technically made it a “quasi-” or “semi-parametric” device. Even today, it would be considered a highly effective equaliser, and by 1971, it was still in regular use at Abbey Road.
The EMI RS56 was physically large and heavy, even bulkier than the Fairchild 660. It featured three vertical control columns for BASS (low), TREBLE (mid), and TOP (high) frequencies. Each band offered three adjustable parameters: frequency selection, amount of boost or cut, and the bandwidth of the effect.
Frequencies: Each band had four centre frequencies:
- BASS: 32 Hz, 64 Hz, 128 Hz, 256 Hz
- TREBLE: 512 Hz, 1024 Hz, 2048 Hz, 4096 Hz
- TOP: 5800 Hz, 8192 Hz, 11600 Hz, 16400 Hz
The ranges were musically chosen, octaves apart in the Bass and Treble bands and half-octaves in the Top band.
Bandwidth (Q): Each band had six shape settings. Four were standard Q types, “Blunt”, “Medium Blunt”, “Medium Sharp” and “Sharp” while two were shelving types, “Low End” and “High End.” The shelves applied to all frequencies above or below a selected point, depending on the setting. The shape affected how wide or narrow the EQ action would be, and shelf settings could interact with other bands when overlapping.
Gain: Each band could be boosted or cut by up to 10 dB in 2 dB steps. The stepped controls allowed precise recall. As a passive unit, the EMI RS56 dropped the signal by 30 dB and required re-amplification, typically via an RS61 line amplifier.
The nearly endless combinations of frequencies, gain and Q led to the nickname “Curve Bender.” The UTC allowed engineers to shape highly complex EQ curves, for example: boosting BASS at 128 Hz with a Blunt shape; boosting TREBLE from 1024 Hz upwards using the High End shelf; and cutting the TOP around 8 kHz with a Sharp setting.
Though originally meant for disc cutting, EMI engineers quickly saw the EMI RS56’s creative potential. EMI’s own guidance described it as suitable for occasional tone control or restoring fidelity to outside material. Their internal recordings, they felt, needed little to no EQ, but externally sourced tapes often did. The RS56 became the go-to tool for fixing those.
Ken Scott recalled first encountering the EMI RS56 while learning disc cutting at Abbey Road. As a trainee, you’d start as a tape operator, then move on to cutting acetates. The UTC became an intuitive training tool, helping young engineers understand EQ through hands-on experience. Initially, many overused it, but over time they refined their approach.
Because of its ability to dramatically reshape sound, the UTC was not commonly allowed on studio sessions. EMI considered such alteration contrary to its “true fidelity” principles. But as the Beatles’ recording approach grew more experimental, the Curve Bender was allowed into the studio. It first appears in photos during the Sgt. Pepper sessions. Engineer Geoff Emerick embraced its potential, and Ken Scott later used it to fix the muddy external mixes of Hey Jude recorded at Trident Studios.
When EMI introduced the TG-series mastering desks around 1970, they created a new solid-state equaliser, the TG12412, to replace the UTC. It preserved the original EMI RS56’s curves and frequencies, easing the transition for engineers and continuing the Curve Bender legacy. Though the TG version is still in use at Abbey Road today, the arrival of these new units marked the end for the original EMI RS56s. Many were discarded, and Brian Gibson recalled seeing one in a rubbish bin outside the studio, a fate shared by much of EMI’s older gear.
