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The legendary sound of the classic EMI / Abbey Road hardware compressor in a modern plugin


Mac / PC compressor plugin. $560 TDM, $335 Native (RTAS / AU / VST)



By Phil O'Keefe




The RS124 compressor plugin




In 1960, EMI purchased several Altec 436B tube compressors for their Abbey Road studios. These were extensively modified by EMI's technical engineers - so much so that they were basically completely new units in terms of their controls and circuitry by the time the modifications were completed. These RS124 compressors (as they were rechristened by the EMI engineers) were later used on practically every single Beatles recording session. Legendary and (since EMI only made a few, and never sold them commercially) exceptionally rare, with a  unique sound that millions of people are familiar with from listening to those classic Abbey Road recordings, it has long been one of the "holy grail" pieces of studio equipment that many engineers have coveted, but only a very few were ever fortunate enough to get a chance to use. Until now…




Abbey Road Plugins set about trying to recreate the sound of these legendary compressors in a software plugin format. There are three different versions of the RS124 plugin included, and each is based on a specific vintage unit that is still in use at Abbey Road Studios today. Peter Cobbin, the Director of Engineering at Abbey Road Studios, compared the original hardware units to the software recreations until he was satisfied with their sonic accuracy, and the "front panels" of the plugins have subtle cosmetic variations that correspond with the specific hardware units that each was based on.




Some of the controls and functions on the RS124 plugin are not readily apparent. For example, clicking on the serial number on the front panel reveals a pop up menu that allows you to select which of the three models (identified by their respective serial numbers: 60050A, 61010B and 60070B) you want to use. (Figure 1) Each of the three Models sounds a bit different, with 60070B having by far the fastest attack and release times. Because of this, it is probably the model best suited for use on individual tracks, while 60050A and 61010B tend to be better suited for bus compression tasks. The RS124 sounds really cool as a bus compressor, and was commonly used in this application at Abbey Road during the 1960s when doing "reduction mixes" - submixing, "ping ponging" or "bouncing down" multiple tracks to a single track to create room on the multitrack tape for new / additional parts. It also functions well as a stereo (or mono) bus compressor for the final mixdown, and adds that gooey sonic "glue" that many engineers look for from a stereo bus compressor.


RS124 3 Models.jpg

Figure 1: Three different models of the RS124 are included; each with somewhat different cosmetics and sonic characteristics.


The Recovery control was an EMI addition to the original Altec design, and can be thought of as a release time control. There are six settings, numbered 1-6, with 1 being the fastest, and 6 the slowest. The exact speed of these is relative, and depends on which Model of the RS124 you've selected, again with 60070B being about three times faster overall than the other two models.


A unique "Hold" control is integrated into the Recovery knob, and is represented by the red dots in between each of the six recovery settings. This feature is very effective for dealing with "pumping and breathing" compression artifacts, and is something I wish more compressors had. It's unique enough that it deserves a more detailed description:


When you have large amounts of compression dialed up, with 10 or 20dB or more of gain reduction - whenever a note fades out or the instrument or vocalist stops, the room ambiance and track noise will "swell up" and "breathe" once the level falls below the compression threshold and the compressor releases the gain reduction. Similarly, large amounts of gain reduction can also cause issues at the very beginning of a track. The RS124 sounds fantastic when pushed hard, but with such heavy settings, the very first note attack will come SCREAMING out at you until the compressor kicks in and lowers the volume level. This "thump" can be 10dB or more louder than the rest of the processed track, and therefore very annoying. The Hold control is designed to deal with both of these troublesome issues, and it does so by providing an extremely long release time; essentially "holding" the gain reduction level for long enough (almost indefinitely) for the last note of the song to fade away cleanly without the increase in noise that is common to most compressors. Once the last note hits, move the Release control to the nearest red dot, and the amount of compression being applied will stay relatively constant, even when the signal level of the track falls below the compression threshold.


But what about when the first note of the song kicks in? How do you deal with that loud initial level thump? You run a a second or two of audio into the compressor and allow it to reduce the gain, then move the Recovery control to the nearest red dot to "hold" that gain reduction level. If you have a bit more gain reduction on the meters than you want, you can manually reduce it gradually by depressing the "Balance" button (located directly below the unit's serial number) until the amount of gain reduction you desire is indicated on the meter. Then just roll back and start the song again. That way, the compressor is already pre-configured for the first note of the track, and you avoid that huge initial spike in output level followed by the big drop-off in volume when the compressor kicks in. Once the first note of the track has hit, you simply move the Recovery control from the red dot to the desired (1-6) Recovery setting. The Hold function is a brilliant idea, and in conjunction with the full automation capabilities of modern DAW software, it makes using the RS124 with large amounts of gain reduction trouble free; without the usual thumps, and pumping and breathing side effects of most other compressors.


The Input Gain control acts as both an input gain and inverse threshold control. Turning it up simultaneously increases the signal level and the amount of compression that is applied to the signal.


The large Meter displays the amount of gain reduction from 0 to 30dB. Each model has slightly different meter ballistics that are based on the unit it was modeled after. One minor cosmetic difference that I noticed is that the plugin versions are missing the Altec logos that the original hardware RS124 units retained on their meters. I suspect this is a licensing related issue, and it obviously has no effect on the sound of the plugins.


Output Attenuation was another EMI addition that the original Altec 436B lacked. It provides the ability to attenuate the output of the compressor in 5dB steps, with the final switch step providing 10dB of attenuation, for a total attenuation range of 30dB. I found that it was sometimes a bit tricky to get the Input Gain and Output Attenuation controls set to give me the amount of compression I wanted without peaking the track or plugin, but a little fiddling usually got the job done, and adding a occasional trim plugin to the signal path - either immediately before or after the RS124 plugin - took care of the few times when I needed to fine tune things further. The control arrangement is not as flexible as fully adjustable and independent input gain, threshold and release controls, but those controls would not be historically accurate, and thus would be out of place on a recreation like this.


However, there is one major addition to the RS124 plugin that was not available on the original EMI hardware units. By clicking on the fuse holder on the unit's front panel, you engage the "SuperFuse" mode. When engaged, the lamp and fuse indicators turn red, and the compressor's Recovery (release time) is set to match the attack time speed. (Figure 2) This results in a much more "aggressive" and modern compression sound. Since the release time is automatically set to equal the attack time, the Recovery control is inactive in SuperFuse mode, but all the other controls of the RS124 function normally, including the Hold function.


RS124 60070B SuperFuse and Hold Modes.jpg


Figure 2: In SuperFuse mode, the release time is set to match the attack time. In this picture, the Hold function is also being utilized to "hold" approximately 20dB of gain reduction.


The on / off Power switch acts independently of the plugin's master bypass button. Why would you need a separate power switch when the host software usually provides a master bypass button? Stereo and LCR instances of the plugin function slightly differently in Pro Tools than they do when running in a AU or VST host. With VST and AU hosts, a single front panel and set of controls is displayed for stereo track instances of the plugin, while in Pro Tools, a dual display is substituted. (Figure 3) This allows Pro Tools users to select different Models (serial numbers) for the left and right channels of a stereo instance of the plugin, and the Power switches allow you to turn each channel on and off independently.


RS124 60050A and 61010B in stereo.jpg


Figure 3: In Pro Tools, stereo instances have dual displays, and different models for each channel can be selected, and even adjusted or bypassed separately if desired.


Rounding out the control panel is the Lamp, which indicates the status of the compressor - white for "on", red for SuperFuse mode, and dark for off.




The RS124 isn't a particularly "fast" compressor; the attack time will seem pretty slow to you if, like me, you were brought up on such speedy American compressors as the Urei 1176. Because of that, it's not always ideally suited for use with drums. By using the 60070B model and engaging the SuperFuse mode, you can get some cool drum sounds out of it, but it might not grab as much of the attack transients as some people may prefer, nor release quite fast enough to fully recover for the next note attack - especially on more uptempo material.


Where I feel the RS124 really excels is with bass, guitars and as a program compressor. It also works very well in "parallel compression" / bus compression applications, and when the SuperFuse mode is engaged, you can get some really punchy sounds from it. The sound is very smooth, with a slight lower midrange thickening that many will equate with "warmth". Slam it hard on bass and guitars, and the source of a lot of "that sound" that you've heard for years becomes obviously clear - the RS124 is a big part of "the sound" that I equate with those classic 60s era Abbey Road recordings. The compression of Rain's bass, Fixing A Hole's lead guitar, the strummed acoustics of the Help and Rubber Soul era material… you will struggle, and ultimately fail to nail those sounds without the RS124... but add it to a recording of an appropriate sound source, and suddenly, there it is.





If you're looking for an extremely fast compressor that can deal with catching the very beginning of quick transients, and releasing fast enough for busy drum parts on fast songs, the RS124 probably isn't for you. It's not a limiter. It is a character compressor, and one with a very distinctive and appealing sonic signature. The Hold function is so effective and useful that it's something I wish every compressor featured. If you're a Beatles fan, and want to recreate some of the sounds of that era, the RS124 is a must have. It really is a BIG part of the sound of their records. Despite its obvious connection to the sound of classic Beatles albums, it isn't limited to emulating those records - remember, these were used on countless Abbey Road recordings by a variety of artists, and not just on the Fab Four's material. The new SuperFuse settings also allow for increased punch and a more modern sound than the vintage units were capable of, further extending their sonic range. While I wouldn't want to have this as my only compressor plugin, after using it for a couple of months, I find it to be indispensable for its distinctive and immediately familiar smooth, warm and punchy sound. The RS124 sounds absolutely wonderful, and you simply can't get its sonic signature from any other compressor plugin that I am aware of.


Want to hear it for yourself and try it on your own material? If you have an iLok, a ten day, fully functional demo license is available, but make sure you have the purchase funds ready to go - once you try this plugin, you WILL want to buy it!



System Requirements:


Windows: XP, Vista or 7
Mac: OS X 10.4 or higher
Pro Tools 7 or higher, or any AU / VST host
iLok Smart Key and iLok.com account

1 comment
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mrtele  |  September 10, 2014 at 11:17 pm


exellent review! Especially when you pointed out the use and importance of hold control. Also which instruments benefit from the use of RS 124. I have never used it paraller comp. setting.  I have to check that out right away. So are you saying this is the warmest sounding plugin in the market. What about Shadow Hill by UA?

Jake Voutilainen

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