Kush Audio UBK Fatso review

  • £2278
  • $2799
The warming effect can enhance a wide range of sources.

MusicRadar Verdict

A sonic enhancement tool that will cast away the digital blues and lave your audio oh-so fat.


  • +

    Big, juicy harmonic distortion. Impressive range of compression characteristics. Sheer depth of tape simulation effect.


  • -

    Very little.

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Kush Audio, in collaboration with Empirical Labs, has taken the original Fatso and adjusted the preset compression parameters (attack, release, ratio and knee) as well as the "saturation-to-compression relationship".

The UBK Fatso comes with the original unit's manual and a guide to what's new in the Kush Audio version, making it clear that the differences are not operational but behavioural.

"The variability of character and response that can be achieved is impressive and deeply rewarding."

The unit is made of four building blocks: a compressor, a soft clipper (harmonic distortion), a 'Warmth' processor (dynamic high frequency filtering) and a transformer (more tape head simulation). These elements allow harmonic and dynamic manipulation that range from the subtle to the outright monstrous.

The compressor is made up of seven combinations of three preset programs (Splat, Smooth and Spank) that are selected with a single button - three LEDs indicate the combination.

The input gain control sets the threshold of the compressor, though this also affects the amount of drive produced by the soft clipper circuit and the depth of the Warmth effect.

To gain individual control over this the rear insert TRS sockets allow an external unit to set the compressor threshold, be it an EQ (for frequency sensitive compression), a preamp or even a foot pedal.

The manuals are quite insistent that utilising the inserts really open ups the range of the Fatso and they're not wrong - once hooked up we never unhooked the inserts, we just altered what was in the signal path.

The roaster

The soft clipper does its harmonic distortion work as you wind up the massive Distressor style input gain knob and to aid your ears there are two LEDs (Comfy and Roast) that light up yellow and red (for 1% and >5% THD respectively) to let you know how much distortion is being produced.

The Warmth processor is essentially a high frequency limiter that simulates the effects of tape saturation. The Warmth button toggles through seven levels, indicated by corresponding LEDs over the button.

Each 'level' increases the high frequency limiting with the corner frequency of the dynamic filter moving up relative to the limiting/attenuation to keep the effect from chopping the top off the audio completely.

The final control before the output knob is the bypass. This not only toggles between the processing and the true hardwire bypass but also engages/ disengages the output transformer.

This is the most subtle part of the Fatso experience, the effect of which becomes apparent with complex sources that have some low frequency presence (e.g. mixes) as the transformer produces most of its harmonic distortion from this range.

This behaviour also affects the mid and high ranges and can bring a slight enhancement or focus to the audio, though this can also shift into a blurring effect with high gains.

The tweaker

Though the compressor is preset, there is a substantial range in use that a single dedicated unit rarely provides and it is easy to control and administer, from subtle mix buss glue to all-out crushing/pumping.

Though a good deal of tweaking happens with the three buttons on each channel the real work is done with the big input and output knobs, adjusting the drive and compensating the final level.

The adjective-heavy legending may seem a little silly but it does belie a sense of fun that comes with operating the UBK Fatso - this is one satisfying tweak-fest.

The variability of character and response that can be achieved with a combination of the seven compressor presets, the seven Warmth settings, the transformer and the continually variable input drive is impressive and deeply rewarding.

The soft clipping input stage can be used do a lot of the work as the distortion smoothes out spiky transients that create that brittle, edgy top end.

Sometimes this can be enough, though with so many sources (especially fat synths and basses) one can easily go through the Comfy region of THD into Roast to really make a source pop out of the mix.

The thickening of the low mids and the transient control that is afforded by this process gives the compressor section a much more even waveform to work from and so very musical gain control can be achieved, especially with the less aggressive Smooth and Glue.

Even with a slightly mellowed transient landscape the Splat and Spank settings really spit and bite, broadening the role of the UBK Fatso into fundamental dynamic shaping. Drums and percussion can smack and pop to the point of pain and with reverb, the results are simply awesome.

The warmer

The Warmth control is something to approach with caution as it can quickly kill the HF life of your audio. With open ears and an eye on the LEDs one can nibble away at the HF spikes to bring in a tape style response that can really smooth the clinical digital characteristic, taking the edge off harsh cymbals or settling an over-bright condenser mic vocal.

When used with care a subtle warming effect can really enhance a whole host of sources, but occasionally an extreme setting can really be just what you're looking for, and the Fatso will easily oblige.

The transformer can sometimes compensate for a loss of HF sparkle as it can excite with a little harmonic distortion of its own.

At the same time the transformer also creates/amplifies harmonics of the low-frequency range and can add a useful thickness and low-mid presence, but this can also manifest as muddiness on already low/low-mid heavy material.

The antidote

There are few hardware products that combine tape saturation simulation with compression (technically they are both forms of the same thing - distortion) and so the UBK Fatso occupies a unique position as a shaping tool.

As an antidote to 'digititus' this is a great piece of gear that will quickly become indispensable throughout the recording and mixing process.

As a more creative means to carve out new sounds, this is a deeply rewarding device that I can imagine finding daily usage, whether in electronic or acoustically generated mediums.

We often employ chains of outboard units to get behaviours that the UBK Fatso seems to easily provide in just a few moves. There are hundreds of compressors out there, and a few tape sims too, but in one box and for this price there isn't anything to compare… well, except the original.

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