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Empirical Labs EL7 FATSO Jr


The inherent non‑linearities and distortions of analogue equipment are sometimes sorely missed in this digital age. Empirical Labs offer their new FATSO Jr as a solution.

The declared intention of the twin‑channel Full Analogue Tape Simulator and Optimiser (FATSO) is to provide the kind of 'softening' and 'warming' that is prevalent in classic analogue preamps, mixers and recorders, and which has always been thought to add so much to the musicality of recordings.

There are a number of processing functions incorporated in this unit, any or all of which may be used together. The 'harmonic generation and soft clipping' is essentially a type of distortion unit which clips signal peaks and makes audio subjectively louder, while a high‑frequency saturation stage allows you to emulate overdriven analogue tape. There is also simulation of transformer input and output circuits, or of the effects of certain types of tape heads, with their generation of fundamentally low‑ and mid‑frequency distortion. Finally, a classic soft‑knee compressor is provided at the front end of the processing chain, offering four different preset operating modes, derived from Empirical Labs' highly regarded Distressor. A full input‑to‑output hard‑bypass facility allows objective assessment of the unit's effects.

F‑plan Diet

Despite its name, the unit is housed in a compact 1U rackmount box, with a rear panel surprisingly well adorned with audio connections, including balanced XLR and quarter‑inch TRS jack sockets, plus unbalanced phono sockets for both inputs and outputs. Each channel also boasts a TRS socket providing side‑chain access for each channel. The mains inlet is the ubiquitous IEC, with its input fuse and voltage selection hidden away inside the case.

Empirical Labs EL7 FATSO JrEL7 FATSO Jr's rear panel connections.

Empirical Labs claim that the front‑panel control arrangement is designed to pack the available facilities onto the front panel without resorting to an LCD screen, and also point out that the LEDs are colour‑coded consistently, with red lights always indicating 'radical or distorted settings'. However, I personally found it rather garish and unintuitive — the quirky design is cluttered and confusing, but I dare say it will appeal to as many as it offends. Moreover, the handbook is almost as poorly structured as the panel, making it difficult to take everything in that you need to know.

The two sets of controls are laid out side by side, with a power switch at the extreme right‑hand end. The first control is a large Distressor‑style Input gain knob calibrated from zero to 10 with a scale graduated precisely in tenths, so there'll be no trouble replicating settings with precision!

A grey rectangular button activates the compressor. Above it, an inverted traffic‑light arrangement of LEDs indicates which of the five basic modes is active: Off, bus, GP (General Purpose), Tracking Comp and Spank. The Spank mode is a fairly firm limiting action, and can be combined with any of the other compression types, though it does naturally tend to dominate in these combination modes. A horizontal row of eight green, yellow, orange and red lights along the bottom edge display the gain reduction, from one to 20 decibels.

A second grey push button sets the degree of Warmth added, with an arc of seven LEDs showing the current setting. A second horizontal row of LEDs, along the upper edge of the panel, displays the amount of HF saturation being applied by the Warmth feature, up to 15dB measured at 20kHz. The scaling is slightly different to the compressor gain reduction meter, but the same colour scheme is employed.

A vertical array of three LEDs comes next along the panel, with the bottom orange one illuminating when the unit is operating in a stereo linked mode. This is activated, rather illogically, by pressing both Warmth buttons together, though a panel legend fortunately reminds you of this! When stereo linked, the side‑chains of the two compressors are combined and the Bypass button of Channel 1 controls both channels simultaneously. However, all other controls have to be matched manually on both channels — input and output levels, compressor modes, and Warmth settings.

The two other LEDs in the column are driven by the Saturation and Distortion Generator. A yellow one (labelled 0VU) illuminates with around one percent THD, and the red one (labelled Pinned) at around five percent THD. With complex mixes the five percent distortion point can be unpleasantly audible, yet with a lot of individual instruments you can drive the unit pretty hard into the Pinned light with entirely acceptable results — a fatter, warmer sound being prevalent with bass, guitar and simple keyboard parts, for example. Having said that, hard clipping occurs just a few decibels above the illumination of the Pinned light, so some care is needed too!

The last button toggles the relay Bypass on and off, as well as inserting the transformer circuit (labelled Tranny) — the current mode being indicated by yet more LEDs. The Output level control uses the same oversized knob as the input.

Piling On The Pounds

Connecting the FATSO Jr into an installation is very simple, if you think of it basically as a compressor. The lack of any input or output level metering can make optimising signal levels a bit hit and miss. However, the handbook suggests Output settings for +4dB and ‑10dBV operating levels, and these seemed to work well enough for me. The input control setting can be adjusted to achieve the desired amount of distortion and compression — there being no threshold control at all. However, you can use a gain adjusting device in the side‑chain to alter operating thresholds if you wish.

My familiarisation with the FATSO Jr started with the Tranny facility. Transformers are notorious for either trashing or enhancing a signal, with frequency and phase response irregularities, saturation, and LF distortion all being inherent to any design. The circuitry used here manages to introduce these kinds of sonic artefacts extremely well, adding fatness and body to sounds, making them louder and fuller in a musically enhancing way. I found it most useful on individual instruments, as full mixes easily became stodgy. Processing low‑tuned percussion, rounded synth bass, or electric bass guitar allowed them to cut through far more effectively, both within a mix and when auditioning the mix on small monitors. For bass instruments, Tranny was more effective and much less invasive than most kinds of simple EQ.

The saturation and distortion element is always active, but its action is very dependent on the input level. The distortion produced is primarily third harmonic, which gives the added bite and crispness often attributed to valve preamps and mildly overdriven analogue tape recordings. The more subtle second‑harmonic 'thickening' is also available, but is principally derived from the compressor circuitry of the FATSO. Again, I found the distortion capabilities of the machine most effective on individual tracks, helping instruments to cut through in the final mix, and also giving overly sterile sources (mainly keyboard parts, I found) a bit of body and sonic interest. Driving the FATSO too hard in a mastering configuration could easily destroy a mix, making it sound messy and fatiguing, so it is essential to constantly reference back to the original sound using the unit's Bypass switch.

Having said this, there are a couple of things to be aware of with the bypass switching. Firstly, the switch also activates or deactivates the Tranny mode, sometimes requiring multiple button presses to achieve the desired condition. Secondly, careful setting of the output level control is required to match the level in the bypass condition, particularly when assessing compression effects. Remember, the ear is easily fooled by the 'louder is better' argument.

The Warmth process looks deceptively simple, but I suspect it is probably the most complex part of the machine. This is a subtle but extremely effective process, which is something like a cross between a high‑frequency limiter and a dynamic equaliser, rapidly taming high levels of HF with both level and filtering adjustments so that only the loudest peaks and transients are affected momentarily. The result is very flattering, and usually worked well with close‑miked instruments. It was amazingly effective on acoustic guitars where it obviated the need for overall compression by elegantly smoothing out the hard edges of string picking noises. You get to keep the natural dynamics of the performance, but lose the headroom‑sapping transients. Increasing the Warmth setting seems to lower its onset threshold, thus taking increasingly more of the edginess (or brightness) out of a track. Consequently, too much Warmth can quickly remove sparkle and immediacy.

The compressor is simple to use, but offers an extraordinary range of effects. The release curve on all compression modes is logarithmic, giving a fast initial recovery followed by a slower rounding out to unity gain, and all modes have slightly different soft knees. The bus mode gives a very gentle 2:1 ratio with slow attack and fast release, delicately controlling overall levels without squashing anything too much. The General Purpose setting combines a medium attack with a slow release and provides slightly firmer level control, while the Tracking compressor has been designed to emulate the classic Urei 1176, which is so effective when recording vocals and a wide range of instruments. These last two modes have to be used with caution if the source has high‑level transients (slapped bass strings, for example) as these can punch holes in the overall level. The Spank function is described as a 'radical limiter' and exerts much greater level control.

The compressor can emulate a range of classic dynamics setups. For example, combining the General Purpose mode with the Tranny option gives a fair imitation of an opto‑compressor — soft, slow and slightly distorted at the bottom end, which is not dissimilar to how my wife describes me, actually! However, when using the FATSO you need to bear in mind that the compressor modifies the signal before anything else, and so its settings interact strongly with those of all the other processing flavours. It is therefore essential to set the compressor first, then the Warmth and finally the Tranny mode. When a lot of distortion is required it is sometimes better to deselect the compression mode, or only to use the bus compressor, otherwise it can be difficult to achieve sufficient drive level. Of course, driving the compressor hard also generates a lot of second harmonic distortion, though it takes a lot to be noticeable on most sources!

Weighing Up

The FATSO Jr is a wondrous machine and, once experienced, you will find it hard to mix or record without one. This is so much more than just another tape saturation emulator, and it can add fantastic new dimensions to flat, lifeless and overly clinical digital recordings. The range of tonal effects available is vast, and they can be optimised easily to almost any instrument or voice. Used judiciously you can simulate very effectively the recognisable effects of valve or Class A semiconductor circuitry, with or without transformer and tape‑saturation effects, though you're not limited to these sounds. The ergonomics and the light‑show may not be to everyone's taste, but the machine is simple to use once its slightly obscure operation is understood.

I found this processor best on individual instruments rather than on stereo mixes, though it can prove useful in this role if used with care. Whether taming the shrill edge of an over‑distorted guitar, or adding psychoacoustic weight to a rounded bass lines, or subtly grunging‑up a lean and sterile vocal, the FATSO can do it all! It certainly impressed me with its subtlety and variety, and I strongly recommend checking it out. Your bank manager might appreciate it, though, if your left your credit card at home...

Under The Hood

Having a look around under the bonnet, so to speak, revealed a well‑constructed chassis with everything mounted on a large main board and a couple of small daughter boards behind the front panel. A nice touch is the provision of a spare mains fuse in a holder adjacent to the live fuse. High quality components appear to be used throughout, but the markings on every single integrated circuit (and there are quite a few) have been carefully erased. No DIY maintenance possible on this machine, then!

The electronics for the two channels are laid out identically side by side, each with five preset trimmers — all unmarked as to their functions. There is also a small audio transformer and a couple of sealed relays for each channel's bypass function. Four DIL sockets in each channel section carry plug‑in caddies with up to eight resistors each, and these are apparently intended to allow various future upgrades or modifications to the processing functions — changing curves and response times, for example. Apparently, registering the product is a prerequisite for accessing information about such possible alterations.

The right‑hand end of the motherboard carries the power‑supply components and the logic control circuitry, complete with a memory‑backup button capacitor. The pair of daughter PCBs behind the front panel carry its LEDs and buttons, and are linked by ribbon cables to the main board. Other than the aforementioned caddies, there are no plugs and sockets interconnecting different parts of the machine — everything is hard wired.

Tape Delay Emulation

One interesting suggestion in the FATSO Jr handbook is to use the processor in a feedback loop around a digital delay, with a high Warmth setting and the Tranny mode switched on. This provides a very effective tape‑loop delay simulation, with those HF losses and distortions that were so much a part of the classic WEM Copycat sound — quite superb with appropriate guitar and keyboard parts.


  • Very effective combination of processes.
  • Comprehensive interfacing.
  • Makes everything sound 'better' with little effort.
  • Stereo linking facility for mastering applications.


  • Messy front‑panel design and ergonomics.
  • You need to set the unit's output level carefully when using the Bypass button to assess the degree of processing, otherwise it is easy to overdo things.


A comprehensive suite of interactive analogue distortions which can turn the leanest and most sterile of digital recordings into the fattest and warmest of sonic luxuries!