This was one of the best purchases I've ever made for my studio. This processor somehow has the ability to make everything you pass through it sound better. It's great for anything from taking the edge off of things to helping a particular track stand out in a mix and can be used in the tracking, mixing and even mastering stages. I really like the compressor as well... very easy to set up and versatile to use on just about anything.
I use this as a bus compressor on electronic (post analog summing) music and it's amazing. I like it more than my API 2500 and SSL G compressor, combined. It does exactly what is described. Mix into bus comp setting around -3/5 dB, warmth on 2 or 3 and mix away. That is the sweet-spot. You will be amazed. It also makes things very loud.
I've used this on basically everything going into the A/D since acquiring it. Definitely fits best first and foremost as a tracking box/drum buss box (i treat it like a fancy distressor w/ fixed comp settings), but I've also used it for mastering applications, and with the lightest touch, you can really make some magic happen. Love this thing to pieces, it's a beast.
I HIGHLY suggest though that if you are considering buying this box that you take it upon yourself to also purchase a cheap effects unit of some sort with gain control and a reasonably flexible eq (i got a dbx graphic eq); the Fatso has a sidechain input on it for controlling the signal the compressor receives (normally just follows the input which means you can't have more broadband saturation without hitting the comp really hard). Having a gain control element to sidechain into it gives you MUCH more flexibility, and with an EQ in the mix you can drop the lows to the compressor for bigger bass (mastering 101), or even make a simple broadband de-esser. Pretty sweet! :)
This makes even the most harsh "digital" sounding recordings sound warm and smooth. I use it to track, mix, and master. It's THAT good. If you do many subtle adjustments of sound with this unit, the layering effect is very special. It sound "professional" the way professional recordings USED to sound before everything sounded harsh and "in a bucket"." Try it!!
The "Skinny" on the FATSO
I need to be physically restrained from using this on everything because it is so addictive! It's incredibly easy to set up and get to work. Even though the buttons have to be pushed multiple times in order to access some settings, it's still very easy and doesn't feel cumbersome at all. The compressor settings are all ok, but the buss compression in particular is great, and so easy to use. The buss compressor is very musical and pleasing to listen to. The Tranny feature sounds good on bass frequencies, but my favorite part of the tranny is the extra edge that my electric guitars get from it. The Warmth controls are awesome - drum samples with a little warmth and compression become much more realistic, harsh recordings can be smoothed out, thin tracks can be fattened. The real challenge with the FATSO is to not use it too much - the individual settings may all sound great, but combined, it may be overkill on a lot of material.
I've used the FATSO during recording and mixing, but my favorite use so far is for mastering.
The warmth and the tranny can be very very subtle, but when used properly, it's really making a great impact on finished product. I'd definitely recommend this to others.