Beatles RS124 and Fairchild 660

Beatles RS124 and Fairchild 660

Agustin Saravia

A puzzling moment the recordist faces when recreating the techniques of the Beatles is that their compressors and limiters lack modern controls to fine tailor this processing. If we know the theory this is far from being a limitation, rather it helps to avoid producing disastrous results. When faced with this scenario the two most important controls on which we shall rely are release time and the gain reduction meter.

Provided we aren't going for a creative result, like the distorted drums in "Revolution" or the gurgling sound of harmony vocals in "Octopus's Garden", compressors are such devices that are used with subtlety for taming peaks and overall loudness. Therefore, in what seems like a contradiction, adjusting compressors by ear may not be the best option. This is due to the main processing being on the attack stage of the soundwave, which goes from the order of hundreds of microseconds to tens of milliseconds. This small time frame is veiled to human ears for identification of loudness levels and time shifts. Our ears start to identify distinct attacks in the order of 1/20 of a second, or 50 ms, for music and a few less milliseconds for speech.

Release controls of compressors usually go from 50 ms to various seconds, hence, their effect is perceived by ear. However, most of the other characteristics of vintage compressors usually have to be relied on the gain reduction meter, which isn't as fast as the soundwave attack but help us to monitor visually what our ears can't.

A rule of thumb for long release times and high compression levels is that they out average each other. High gain reduction levels get away with short release times and long release times get away with low gain reductionn levels. Therefore if we are processing a mix or submix of instruments, each with different attack times, a long release time and low gain reduction of -1 dB helps to avoid the compressor ducking on the attack of every instrument and then being obvious. On the contrary, if we are trying to tame an instrument with inconsistent levels a greater gain reduction of -3 to -10 dB may be of help but using a shorter release time.

The same could be said of attack times, and that's the reason at EMI Studios the slow attack of the EMI RS124 was preferable for mixes and rhythm instruments while the fast attack of the Fairchild 660 was preferable for lead instruments.

In the next examples the compression meter is as important as the release time setting. The other controls are of less interest.

1  Mixer Bus and Audio Program

During the Beatles 4-track years, i.e. 1964-1968, the EMI REDD.51 mixer usually featured a matched pair of RS124 and a pair of 660 inserted before the faders of busses I, II, III, and IV respectively. Busses I and II featured RS124 while busses III and IV featured 660. Due to the gain structure of the REDD.51, the RS124 and 660 were hit by a signal of -14 dBm. This gain would be equivalent to -32 dBFS in the digital domain when 0 dBm is aligned with the old EBU standard of -18 dBFS (i.e. -18 dB - 14 dB = -32 dB).

Table 1. Bus, Compressor Type, and Audio Program

Bus Device Program
I EMI RS124 Stereo mix L, mono mix, drums and bass (1964-1965), bass (1966-1968), rhythm section (1966-1968).
II EMI RS124 Stereo mix R, rhythm gtr. (1964-1965).
III Fairchild 660 Perc., gtr., vocals.
IV Fairchild 660 Drums (1966-1968), vocals.

Fig. 1a. Ardour emulating a REDD.51 mixer. The center section shows RS124 and 660 plug-ins inserted before faders (Blue) of busses I, II, III, and IV.

Fig. 1b. A pair of RS124 and a pair of 660 plug-ins in Ardour.

2  EMI RS124

The Altec 436B is a variable µ compressor designed in 1958 for radio broadcasting applications. It features an input gain knob as single control, an attack of 50 ms, a release of 1,000 ms, and a ratio of 2.5:1 at maximum compression. Led by Len Page, engineers at EMI Hayes modified the 436B by adding a stepped bridged-T output attenuator, a six-position recovery switch, and trying different values of the capacitor C4 until finally settling on 0.5 µF in 1963, shortening attack to 25 ms and release to 500 ms. Three RS124 units survive to this day at Abbey Road Studios, bearing serial numbers 60050A, 60070B, and 61010B.

Table 2. Altec 436B and EMI RS124 Specifications

Model Attack (ms) Release (ms) Ratio
Altec 436B 50 1000 2.5:1
EMI RS124 25 500 2.5:1

Fig. 2a. 436B.

Fig. 2b. RS124 serial No. 60050A and 61010B at Abbey Road Studios.

Fig. 2c. Schematic of 436B. Attack is C4 x R12, release is C4 x R9, C4 is 1 µF.

Fig. 2d. Schematic of RS124. Attack is C4 x R12, C4 is 0.5 µF.

2.1  Compression Ratio

Being a variable µ compressor, the ratio of the RS124 is 2.5:1 at maximum compression.

Fig. 2.1. Ratio of Cool Stuff Labs RS124 plug-in is 2.5:1 at maximum compression. Threshold is -68 dBFS.

2.2  Control Settings

In every photograph of the Beatles in the studio control room the RS124 features consistenty the same settings: Recovery 1, Input Control at 3, Output Attenuator at 0 dB. This results in -1 dB of gain reduction when a line-up tone of -14 dB is fed to the input. Ken Scott recalls that for mixes and most of the time the gain reduction needle almost barely moved, it just tickled in the signal peaks. Emerick wrote down -10 dB of gain reduction for dilruba in "Within You Without You". Hence, balance technicians at EMI Studios aimed for greater gain reduction for individual instruments (e.g., bass gtr., rhythm gtr.) than for rhythm section.

Table 2.2. Audio Program and Gain Reduction

Program Recovery Input Control Gain Reduction (dB) Output Attenuator (dB)
Mix 1 3 -1 0
Rhythm Section

Fig. 2.2a. Settings for rhythm section and mixes.

Fig. 2.2b. K. Hasebe, session for "Yesterday", EMI Studios, Jun. 15, 1965.

Fig. 2.2c. L. Eastman, session for "Why Don't We Do It in the Road", EMI Studios, Oct. 10, 1968.

Fig. 2.2d. E. Russell, Let It Be sessions, Apple Studios, Jan. 23, 1969.

3  Fairchild 660

The Fairchild 660 is a variable µ compressor designed in 1959 for disc cutting. It features two attack settings of 0.2 and 0.4 ms, six release settings ranging 300 to 5000 ms, a maximum ratio of 20:1 depending on input gain, and two threshold points, a limiter threshold, or DC threshold, and a compression threshold, or AC threshold. Engineers at EMI Hayes modified the 660 by replacing the input gain knob with a stepped -55 dB attenuator to precisely recall input gain settings, a feature useful for classical music sessions spanning through several weeks. As with the RS124, the 660 were modified and calibrated in matched pairs to funtion in stereo when side chained. This feature allowed some interesting effects, like the gurgling backing vocals by Harrison and McCartney during the guitar solo in "Octopus's Garden", which are compressed when triggered by bubbles blowed by Ringo through a straw in a jar glass.

Table 3. Fairchild 660 Specifications

Model Attack (ms) Release (ms) Ratio
Fairchild 660 0.2 300 20:1
0.4 2000
0.2 1000

Fig. 3a. EMI modified 660 serial number 519 at Abbey Road Studios.

Fig. 3b. Schematic of 660.

3.1  Compression Ratio

Being a variable µ compressor, the ratio of the 660 is 20:1 at maximum compression. AC threshold, or compressor threshold, is set by the user by means of a control knob on the front panel. DC threshold, or limiter threshold, is set from factory by means of a screw knob mounted on the chassis inside the housing.

Fig. 3.1a. Ratio of Waves Puigchild 660 plug-in is 2:1 with threshold set at 10, equal to -32 dBFS.

3.2  Control Settings

In every photograph of the Beatles in the control room the 660 features the same settings: Input Gain at -14 dB, Threshold at 7, Time Constant 2. Instruments with long sustain benefit from -3 to -5 dB of gain reduction. Drums need subtle amounts of only -1 dB to enhance the sustain of cymbals.

Table 3.2. Audio Program and Gain Reduction

Program Gain Reduction (dB) Input Gain (dB) Threshold Time Constant
Vocal -3 -14 7 2
Drums -1 3

Fig. 3.2a. Settings for vocal.

Fig. 3.2b. Settings for drums.

Fig. 3.2c. E. Russell, Let It Be sessions, Apple Studios, Jan. 23, 1969.

Fig. 3.2d. E. Russell, Let It Be sessions, Apple Studios, Jan. 24, 1969.


[1]  436B Amplifier, Altec Lansing Corp., Anaheim, CA, US, 1960.
[2]  Model 670 Stereo Limiter, Fairchild Recording Equipment Corp., Long Island, NY, US, 1959.
[3]  B. Kehew and K. Ryan, Recording the Beatles, 2nd ed., Houston, TX, US: Curvebender Publishing, 2010.
[4]  M. Lewisohn, The Beatles Recording Sessions, New York, NY, US: Harmony Books, 1989.
[5]  A. Nisbett, The Sound Studio, 7th ed., Waltham, MA, US: Focal Press, 2003.
[6]  L. Page, RS.124 Compressor Amplifier (Altec), EMI, Hayes, UK, Drawing No. RS.124/D1/2, Apr. 2, 1965.
[7]  K. Scott and R. Owsinski, Abbey Road to Ziggy Stardust, Los Angeles, CA, US: Alfred Music, 2012.

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