Since nobody else has answered I will give it a shot.
Here is some great info about FA from a couple of knowledgeable hunters...
http://www.findmall.com/read.php?37,2106936,2107625
My take on it all is this has to do with speed of the processors.
On my F70 I have DE speed and SL speed...DE is default, SL is for slow and moving the coil slower is recommended.
Comparably some of the F75's have DE and Boost....plus now FA, fast process, which was mentioned is about 1/3 faster than DE.
I can see a difference in mine between DE and SL...how fast this FA is would probably blow my mind if I ever tried it because DE is blazingly fast for me when using it anywhere but especially in iron or trash infested sites.
The best use for these speedy processes is in unmasking but with a bit of depth loss, the slower speeds like my SL or Boost on the upgraded F75's are said to get a little bit more depth.
This has to do with what engineers call sampling...how much time the system uses to process what it sees.
More time spent examining what's in the ground deeper will give you a clearer picture or in our case more useable data.
They say it is like taking a picture or snapshot.
Take any camera, point it at the night sky and leave the lens open for different time lengths.
The more time you leave it open the more time the light from distant stars have to register and be recorded.
The more time that elapses with an open lens the more stars.
Regarding detectors slower speeds equals greater depth and accuracy.
When using a detector in a trash filled or iron filled site this slow speed can be a detriment.
A much faster reaction time is much better for getting better usable data when good targets are in the vicinity of bad ones in order to tell them apart.
Tone choices have a lot to do with this too.
In that thread Keith Southern talks about using 2 tones...I myself prefer monotone as it seems to have the fastest reaction time for me especially using DE.
That is the holy grail target for detector manufacturers...designing units that can give us the most accurate info on all targets and in all situations both deep and shallow but none that I know of have reached perfection as of yet.
You might have heard the Deus is very good for hunting in iron infested sites.
This has to do a lot with its superior processing speed but other brands are no slouch in this area either, some are slower but designed that way for specific reasons.
Minelabs are known to recover very deep silver coins very well especially in less dense and trash and iron filled sites but slow movements of the coil are paramount to take advantage of their abilities.
I use Fishers and Tesoros because of many reasons but recovery speed is the primary one...I tend to be a naturally fast swinger and have to watch myself constantly and I also spend a lot of my time hunting very crowded trash and iron infested sites.
I found a large gold nickel area ring with only about 10 hours experience on my new F70 in a trashy picnic area a few years ago.
DE speed, 4H tones, it had trash very near on both sides very close but I still heard a fleeting high tone in that combination and pretty jumpy signal which made me stop, notice and examine it further and then dig it.
With slight movements of the coil I got that high tone to repeat just enough to trigger my digging instinct.
If I was using a slower machine, moved the coil any faster or used a detector with any less separation abilities I am sure I would have missed it.
I can't say for sure but if I had that FA process at my disposal that ring might have stood out even more than it did for me in DE...I might have missed it completely in SL for all I know.
It might have been way more obvious than it was at that time with a faster process because that high tone was extremely short.
It has been a few years now and I have had much more experience hunting in ridiculous amounts of trash and iron with my Fisher using 3 different coils and I have been surprisingly successful with SL and especially DE.
It took time and patience to learn how to do this, very slow coil movements too, but my jaw has dropped consistently...with FA process hunting in all of my sites I might have done even better.
As far as your instability using FA at your sites try reducing the sense and thresh levels a bit and try different combinations.
These settings are connected and have a relationship that affect the signals we get at all depths not to mention chatter and noise.
I have used many combinations and have been surprised at some things.
For instance sense set into the 80's or 90's and thresh set at -4,5 or 6 still seems pretty quiet, gets me pretty deep and can still find coin and ring sized targets at depth.
I have used lower sense too and done well, experimenting is fun for me and I have a whole slew of different settings and combinations I locked into memory and use and have been successful using pretty much all of them.
Fishers are way overpowered out of the factory and the gain settings are not what you might think like they are on other brands where more power equals greater depth.
75 is not 2/3rd power level, 50 is not 50% power, 33 is not 1/3rd power and so on...they are all much more than they seem and don't work at all like a volume control on a stereo.
There is a member here with an F70 and a vid on YouTube that was still able to hit an 8" coin in his test garden with his sense set on...1.
Use FA or any other process, adjust the sense and thresh to noise levels you feel are comfortable and look for targets at all depth levels.
You might be surprised on what you see, hear and experience.
