Empirical Labs FATSO

Apr 1, 2001 12:00 PM, BOB BUONTEMPO


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The FATSO acronym stands for Full Analog Tape Simulator and Optimizer. However, that only partially describes the effects and features offered by this unique piece of audio gear.

Designed by Dave Derr, FATSO is the latest product offering from his company, Empirical Labs, manufacturers of the well-known EL-8 Distressor, a favorite of many producers and engineers. It's my first choice in several situations that call for the use of a compressor.

After months of hearing rumors floating around the industry concerning FATSO, it was with great anticipation that I received one of the first production units for review.


The EL-7, as the FATSO has been designated, is a 2-channel, digitally controlled, analog signal processor, capable of stereo or dual-mono operation. The front panel has four large, calibrated knobs that go up to 10 — not quite Spinal Tap, but very close. Two of the gray knobs are used for Input Level and two for Output Level control. Three buttons per channel (the Compression Selector switch, the Warmth/Link switch and the Tranny/Bypass switch) and a host of LEDs for metering and status indication completes the package.

Inputs and outputs are via XLR or ¼-inch TRS jacks, with the XLRs differentially balanced on the inputs and outputs and the ¼-inch jacks balanced on the inputs as well. Pin 2 is wired “hot” on the XLRs and is user-changeable to Pin 3 from inside the unit. The owner's manual makes a point of stressing that the unused pin of a single-ended XLR output cable should be “floated” rather than tied to ground to prevent shorting out any of the output amps. I checked with the factory about this, as many potential owners of the unit may use off-the-shelf cabling for their wiring needs. In many instances, pre-wired XLR to ¼-inch cables have the unused XLR pin tied to ground on the minus side. This is true especially if they are of the unbalanced, two-conductor, musical instrument-type. The manufacturer replied that this would only present a problem if a combination of XLR and ¼-inch jacks were used simultaneously. In case of doubt, Empirical Labs offers optional (correctly configured) XLR to ¼-inch adapter cables.

No digital inputs/outputs are provided, even though the targeted market is obviously the DAW, MDM and hard disk recording contingency. I thought about this for a while and decided it was a good thing. Because this is an analog processor, you'd eventually have to convert your digital signal to analog to use this unit, anyway. If Empirical Labs had included an AES or S/PDIF provision, then not only would the price increase, but you'd be forced to use their converters, however good or bad they were, instead of the converters you already own and love. This way just saves you a decision and a step. If you don't want to ever leave the digital domain, then this is probably not the unit for you at mixdown, but it certainly could be helpful during tracking sessions.

A Link/Sidechain input and individual channel inserts are also provided via ¼-inch jacks. The power cord is the IEC-removable type, and an internal switch can change the operating voltage from 110 to 220 VAC.


The one-rackspace unit is solidly built, and the quality, craftsmanship and heft of the box will be immediately apparent. But, after all initial impressions are expressed and descriptions of its physical layout are noted, two burning questions about FATSO still remain: What the heck does this thing do, and how does it sound while doing it?

What it does is not an easy question. The short version is that it emulates the characteristics of an analog tape machine when mixing and/or tracking digital signals to help “warm-up” their sound. Unfortunately, these days, “warm” is probably the most overused term for defining a desirable characteristic pertaining to a piece of audio gear.

A better — albeit longer — answer requires describing the types of processing the FATSO has on-board, while noting that they can be used individually or in combination. Oh yeah, it sounds so sweet when performing all of these functions, as well.

The first process the FATSO offers is Harmonic Generation/Soft Clipping or Distortion Generation. This produces continuously controllable second- and third-order harmonics, which, when added to the signal, provide a richer, fuller sound. There is also an apparent increase in volume without an increase in level.

Many software plug-ins try to achieve this effect in the digital domain. However, the ones I've tried usually sound like they are just overloading the system's electronics to unusable (and unlistenable) proportions. I find that this happens no matter how much its GUI looks like the controls of an analog tape machine.

Without giving away any of his design secrets, Derr stated that digital processing cannot be used effectively when creating clipping and distortion generation for frequencies above 3 kHz without a byproduct of unpleasant artifacts. He believes that only if current sampling frequencies are greatly increased will digital signals ever hope to rival the resolution that can be achieved for those purposes in the analog domain.

The FATSO, however, does this job so nicely that once you patch it in and tweak it up, you'll have a hard time ever taking it out of the chain.

The unit does add distortion to the signal, but it is perceived as harmonics — not as overload. The second harmonic generated is the equivalent of an octave above the fundamental tone or pitch, and the third harmonic is a fifth above that. This process adds body and clarity to the mids, while “tightening up” the bottom, which is especially noticeable on smaller speaker systems. The bass will seem more defined, and, generally, the other instruments and vocals will be more “in your face.”

Of course, this effect, like all the processing in the unit, is a bit like hot sauce; a little goes a long way, and too much will kill the taste of what you are cooking up.

The Harmonics and Soft Clipping are always in the signal path, unless the unit is bypassed. The effect is controlled by the amount of input level the FATSO gets, as adjusted by Input Level pots. This may be a problem for some users. You always get the effect when you put anything through the box. Because that is the main purpose of the FATSO, I don't have a problem with the setup. Still, be aware that this is the case when using the device.


Four types of compression, with seven possible combinations, are served up next. These have fixed-time constants and ratios, and the amount of gain reduction is, again, dependent upon the input level. The compression, however, can be bypassed from the circuitry with the Compression Selector switch. Two LEDs on the front panel of each channel indicate the “0 VU” and “Pinned” status of the FATSO. These can facilitate setting the input levels for the Compressor, Harmonics Generator and Soft Clipping processes.

The manual notes that if compression is being used, then it should be the first process set up. The rest of the unit's functions should be adjusted relative to the compressor's settings. I found this to be critical.

The compression has that famous Empirical Labs quality, only without the more extensive control of the Distressor. But, if you use one of FATSO's compressors carefully and gently, the parameters that you've chosen work just fine for both tracking and mixing.

The four types of compression start with the “Bus” mode. If the FATSO consisted of only this compressor and the Harmonics/Soft Clipping Generator, then I still would have been sold on the thing. When placed across the stereo bus of a mixer or on playback of a 2-track source, you can't help but smile. I found material I previously mixed with a bit of low-end boost could be remixed through the FATSO, without the low EQ, and have a fatter, tighter bottom.

The “Bus” compressor is designed to emulate an SSL Stereo Bus compressor and, when used gently, does a nice job of transparently pushing up your level a tad, without pumping or other nasty side effects.

The “General Purpose” compressor is the next type up on the menu. Having a little faster attack, I found it a bit heavy-handed for the stereo mix, but nice for printing tracks — sort of like a dbx 160X.

The “Tracking Compressor” is meant to emulate an 1176 and does a good job. This sound is the closest that FATSO comes to matching the Distressor. With its controls set for fast attack and release times, I found this setting the most useful of the compressors for individual instruments.

Finally, “Spank” is a high-ratio compressor/limiter having the characteristics of the compressor on an SSL talk-back mic, but with full bandwidth and better overall specs. It has an “over the top” sound when hit hard by a signal. Spank can be used alone or as a peak limiter following any of the other compressors.

The Compressor Selection switch cycles between the different compressor types, allowing one switch to choose any of the four compressor types individually, or to select Spank along with one of the other three in series. It also can bypass all of the compression. Distressor users will be familiar with this type of multiplexed switching.

The “Warmth” (there's that word again) processing is an interesting and unique function. Its control steps through eight stages, starting with off, then, as marked by LED indicators, from one to seven. Each degree of added Warmth causes more gain reduction, from a frequency-dependent limiter with a lightning-fast attack and release. The filter controlling the response of the process is carefully designed to lop off only the highest, shrillest frequencies very quickly and recover just as fast. When used judiciously, this truly mimics analog tape saturation and self-erasure. Most of the frequencies affected by the Warmth process are above 10 kHz. This helps tame “spitty” vocals, harsh, edgy cymbals, overly bright guitars, trashy tambourines and other signals that may not respond well to the digital recording medium.

The Warmth control and the compressors are heavily interactive, so, again, the compression should be set up first when using these processes together.

Both FATSO channels can be linked for stereo, or multiple units can link together for 5.1 mixes. Unlike most other stereo units, the inputs and outputs on each channel are still individually adjustable. This allows tweaking the levels on both channels independently. However, to maintain good stereo imaging, the Input and Output Control settings on both sides should be matched.


The final FATSO process involves an actual iron and coiled wire transformer, known as the Tranny. This transformer is unlike those used on older (and some current) tube and Class-A gear to isolate and impedance-match the inputs and outputs of equipment. They imparted their coloration on the sound of the gear, unintentionally, by being a necessary evil in the circuit. The Tranny process is intentionally designed to add certain characteristics to the sound. In a nutshell, it adds a midrange bite while it softens transients and tightens up, yet increases the apparent loudness, of the bottom.

The Tranny/Bypass Control switch is used to toggle the Tranny in/out of the signal path. This may be a point of contention for some people. In order to fit everything on the front faceplate of the unit and still use the same type of switches throughout, the Tranny shares control buttons with the Bypass function. So, when using the true, hard-wired, relay-controlled Bypass on the box, one must first switch through the Tranny function, if it is not engaged. If returning to the Tranny from a Bypass condition, then another two taps of the switch are required. The same system of multiplexing and cycling used on the other control buttons is employed, but instead of moving through two steps of the same function, it steps through two separate functions. I got used to this and it is no big deal, but some may find this a weak spot on the FATSO.

The manual suggests a test for the Tranny process that is fun to try and will impress your friends, family, clients and pets. Send a 40Hz sine wave through the unit, and match the levels with and without the Tranny bypassed. Now, pull out those Auratones, or any other little speakers you've got, and monitor the tone without the Tranny engaged on those guys. Then kick in the Tranny process. I won't give away the results.

A few clever tips are mentioned in the manual, as well, which only add to the versatility of the unit. By inserting a device with level-controlling abilities in the insert point of a channel, you can raise or lower FATSO's threshold by changing the level of the inserted device. When you add gain at the insert, the threshold of the unit is lowered and the amount of distortion produced is less. The opposite holds true when the gain at the insert is lowered. Of course, the inserts can be used in the regular manner, too, to add an EQ or some other device in the chain.

Sidechain processing is also available using the link outputs to send signal to an equalizer and returning the EQ's outputs to the link inputs of the same channel.

During mixdown, a good way to use the device is to set FATSO across the stereo bus before any other EQ, compression or effects are added to the individual tracks. You'll probably use less signal processing that way: FATSO becomes a sort of Exciter in reverse, adding honey to your mix.

The Compressor types have been designed with “headers,” which permit different value components to be swapped with the existing ones in the FATSO. These will allow the control of the time constants, ratio, threshold and other characteristics of the compressor to be changed and/or custom-modified in the future as they are offered.

At $2,499, the FATSO should be considered by users of digital audio systems — DASH, DAWs or MDMs — who want the perfect unit-to-track through and for use across the stereo bus at mixdown. Analog audio users will find this another quality tool for their arsenal. Anyone who has longed for a 1-inch, analog, 2-track machine should check out a FATSO, as well.

Empirical Labs, dist. in the U.S. by Wave Distribution, 1170 Greenwood Lake Turnpike, Ringwood, NJ 07456; 973/728-2425; fax 973/728-2931; www.wavedistribution.com or www.empiricallabs.com.

Bob Buontempo is a freelance engineer, producer and writer based in the New York City area. His new goal in life is to make enough money to eventually put himself in a good nursing home. You can contact him, harass him or donate to his cause by e-mail at THEMIXFIX@aol.com.

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