UAD EL7 Fatso Plug-in Analysis

UAD EL7 Fatso

Fatso offers a wide palette of possibilities for adding fat analogue character and cohesiveness to your tracks and buses.
The Input stage allows you to dial in subtle to extreme amounts of harmonic saturation and soft clipping.
Inject the warm, musical qualities of magnetic tape, tubes, and class A transformers to instruments or entire mixes.

Soft Clipper and Harmonic Generation
Driving the input stage of Fatso will gently soft clip the source. This process is great for smoothing sharp peaks and transients. As a consequence of symmetrically soft clipping the waveform, Fatso generates low-order even and odd order harmonic distortion, which is weighted towards the third - very reminiscent of tape saturation.
The ‘Warmth’ circuit simulates the high-frequency saturation and self-erasure effects generated by analogue tape machines. As Warmth is increased, excessive high-frequency content and transients will be rapidly attenuated. The time constants are almost instant, therefore the signal quickly returns to unity after attenuation.
The ‘Tranny’ circuit emulates the musical, non-linearity of input and output transformers, including low-order saturation, inter-modular distortion, frequency rounding and transient clipping.
When Tranny is enabled, the circuit will generate higher order harmonics, which sound more edgy and aggressive compared with their low order counterparts.
Fatso offers four soft knee compression types that sound very smooth and sweet. The compressor types can also be combined to create a more ‘in your face’ sound.
The release curve of all compressor types is logarithmic; therefore, it releases quickly at first and then slows as the signal approaches unity – very reminiscent of the release characteristics of the Teletronix LA-2A.
Buss - gentle 2:1 ratio with soft knee and slow attack and fast release time constants. This compressor is very smooth and transparent sounding, 1 - 4 dB of compression is typical for mix bus processing.
G.P. (General Purpose) – medium attack and slow release time constants, G.P. sounds relatively transparent while able to maintain a consistent RMS level. The slow release will not pull things into your face unnaturally.
Tracking – an 1176 type compressor with fast attack and release time constants. This compressor type is great for tracking instruments and vocals during the recording stage or at mix down.
Spank! – is a limiter that musically squashes the dynamic range. There is a subtle knee followed by hard limiting. Spank was specifically designed to emulate the squeeze of the old SSL talkback compressors from the 70s.

Setting Fatso Up – on Fatso Sr. you should always start by setting the desired amount of input drive and saturation. Enable the compressor and choose the appropriate compressor type for the source material; adjust the side-chain filter, attack and release constants, and threshold parameters in the lower panel to set the desired amount of gain reduction. If using Fatso Jr. simply set the compressor up first with the input gain control. It is worth emphasising that you should always set the compressor up before the Warmth and Tranny processors, as the compressor heavily interacts with these circuits. Set the desired amount of Warmth, if any; and then continue by enabling Tranny if you required transformer like saturation. Tranny low-frequency saturation, which is reminiscent of the low-frequency head bump produced by analogue tape machines, can be adjusted in the Fatso Sr.’s lower panel. Complete the process by setting the desired output gain.
Distortion Box – Fatso can be utilised as a harmonic saturator and soft clipper. Simply bypass the Compressor, Warmth and Tranny circuits and drive the input to taste. However, adding a little ‘Warmth’ sounds very pleasing and can soften harshness introduced by heavy saturation.
High-Frequency Saturator – Tranny is great for subtly softening excessive transients and sources that have a brittle edge.
EQ Tamer - for sources that are overly bright or have 10KHz and above boosted heavily with an EQ, Warmth is by far the best choice. It’s almost instant time constants enable it to get out the way in less than a millisecond.
Low-Frequency Playback – as a consequence of the low-frequency saturation imparted on the source; Tranny is excellent for enabling pure low-frequency content such as sub bass to cut through a mix on small speaker systems.

To analyse the non-linear behaviours of the Fatso, I ran a 100 Hz sine wave through the plug-in at various settings.

100 Hz sine wave at -12 dB passed through Fatso Input at +12 dB

100 Hz sine wave at -12 dB passed through Fatso Input Overloaded, Output compensated

100 Hz sine wave at -12 dB passed through Fatso Input at Unity and Output boosted

100 Hz sine wave at -12 dB passed through Fatso I/O Unity with clean gain post processing

Fatso generates low order even and odd ordered harmonics, which are heavily weighted towards the third. The harmonic distribution of Fatso is reminiscent of tape, hence its fat and rich sound character.
As you can see above, harmonic generation is input level dependant. The output of the Fatso is clean gain (or is it?), since the Fatso boosted output and clean gain boosted output are identical.

100 Hz sine wave at -12 db passed through Fatso Input at Unity, Tranny engaged, output compensated

The Tranny circuit generates a lot of high order harmonic components, perhaps this is why I have never liked its effect on the master bus. However, I think this circuit will have many uses when mixing. High order harmonic distortion, especially above the seventh, gives a sound edge or bite. These characteristics tend to reinforce the fundamental, giving the sound a sharp attack quality.

For this test I ran a drum loop through Fatso at various settings. I have compensated for level so that the drum loop peaks at -1 dBFS for maximum resolution of the waveform in Pro-L.

Dry Drum Loops -12 dB

Drum Loop at -12 dB passed through Fatso Input at Unity, output compensated

Very subtle soft clipping behaviour that sounds great!

Drum Loop at -12 dB passed through Fatso Input at 0VU, output compensated

Slightly more transient rounding with some high frequency emphasis, take a look at the hats.

Drum Loop at -12 dB passed through Fatso Input Pinned (heavily overloaded), output compensated

Lol, a picture says a thousand words…

Dry Drums
Fatso Dry Drums.aif (678.3 KB)
Fatso at Unity
Fatso at Unity.aif (678.3 KB)
Fatso at Unity with Warmth
Fatso Drums Unity with Warmth.aif (678.3 KB)
Fatso at Unity with Tranny
Fatso Drums Unity with Tranny.aif (678.3 KB)
Fatso at Unity with Warmth and Tranny
Fatso Drums Unity with Warmth and Tranny.aif (678.3 KB)
Fatso with 0VU Input LED lit
Fatso Drums Input 0VU.aif (678.3 KB)
Fatso with Pinned Input LED lit
Fatso Drums Input Pinned.aif (678.3 KB)

Dry Bass Loop
Fatso Bass Dry.aif (1.3 MB)
Bass Loop through Fatso Input Pinned with Warmth and Tranny
Fatso Bass Dry.aif (1.3 MB)

Listen to that sub growl! Fatso adds body and depth to the bass.

Lets take a look at Fatso’s frequency and phase response at various settings
What I am looking for is the frequency and phase response of the plug-in at unity and how particular settings change this relationship.
Spectrum Colours
Yellow - noise generated by the plug-in analysis software to analyse the plug-in
White - frequency response of the plug-in at that particular setting
Red - phase shift of the plug-in at that particular setting

Fatso at Unity

Fatso at Unity with Warmth at 4

Fatso at Unity with Warmth at 7

Wow! There is a huge difference in frequency and phase response between these two settings.

Fatso at Unity with Tranny

Fatso at Unity with Tranny at Max (lower panel)

Fatso with Input at Maximum

Fatso with Output at Maximum

Although Fatso Output does not generate harmonics or saturate, it certainly is not clean gain!

Fatso with Maximum I/O settings

Nice curves!


Interesting. Thanks.

Another amazing analysis… thanks Paul! I have hardware Fatso in my studio. If you send me picture with your settings I can process same audio material via my Fatso unit and we can see how it compares to UAD.

Amazing Paul! Incredibly detailed yet concise analysis here. FATSO is (almost) always in the mastering chain these days…green light only (buss compressor mode), a gentle amount of drive, internal sidechain filter at 480, and 0,1, or 2 on the warmth…it take the digital glare off of mixes but with a modern, not vintage sound. Please keep these coming! Brilliant!

That sounds awesome! I never used the hardware before, look forward to hearing the results.

Yes, same, you got me to revisit the Fatso again and damn I like that sound!


What about doing one for the chandler zener limiter?

I will do, I am in the middle of a couple now and will take a look at the Zenor after these.