http://u.cubeupload.com/johnedmonton/ATMaxFullSensitivity.jpg
As previously mentioned, adjusting the threshold, to hear those soft whispers of deep targets and also to accommodate people with hearing loss, allows the user to get very deep targets and/or tiny targets often missed by others. This ability to hear those soft whispers benefits those hunting for gold nuggets, especially tiny ones. It also allows relic hunters to search deep. Deep targets are generally older. Often times, all you hear are soft whispers or a change in audio using the audio threshold. Should you dig those targets? Absolutely! For this air test I had the threshold set at +2, where I could hear a constant background hum. Measuring the distance from where a audio signal begins to repeat itself is where I tracked the distances today. I performed the air tests today in my backyard, where I could run the AT Max at full sensitivity. And what a difference it did make.
The above pic shows the depth (in inches) for the shown targets. I was using the true all metal mode, with the iron audio turned off. It is by far the deepest mode, and should be used when searching for known deep targets and areas not too trashy. It is also the preferred mode searching for those tiny nuggets, easily missed by other metal detectors.
http://u.cubeupload.com/johnedmonton/237ATMaxFullSensitivity.jpg
Here is an air test using the zero discriminate mode. Again, it was set up using a threshold set at +2, noting soft whispers or a change in audio using the audio threshold. These again were the measurements that were used. Although not as deep as the true all metal mode, it still maintains a very good depth. And don't forget, that the AT Series have some of the best tones to ID targets correctly.
http://u.cubeupload.com/johnedmonton/d6eATMAXItemstestedGRAP.jpg
Here is a histogram comparison graph showing the differences in depth. It's all a mater of how a user utilizes his metal detector. On the one hand, a user can metal detect, hear those obvious good target ID sounding items and cherry pick the easy ones. However, those looking for those rare, well sought after targets will take advantage of the new Garrett AT Max's ability to sniff those extremely deep targets, often times missed by others.
Below is a pic of my air test target set up to pull out those numbers today. Remember, the air tests show a targets maximum potential. Depths will very from location to location. If a target has been in the ground for a very long time, part of it's surface may have broken down, leaching into the soil around it. The detector coil may read this as a larger target, allowing it to penetrate even deeper. To maintain a high level of reliability, I wore no watch, rings, belt and emptied my pockets. All targets were observed several times to make sure that the most accuracy was maintained for measuring repeatable audio at proper depth.
As previously mentioned, adjusting the threshold, to hear those soft whispers of deep targets and also to accommodate people with hearing loss, allows the user to get very deep targets and/or tiny targets often missed by others. This ability to hear those soft whispers benefits those hunting for gold nuggets, especially tiny ones. It also allows relic hunters to search deep. Deep targets are generally older. Often times, all you hear are soft whispers or a change in audio using the audio threshold. Should you dig those targets? Absolutely! For this air test I had the threshold set at +2, where I could hear a constant background hum. Measuring the distance from where a audio signal begins to repeat itself is where I tracked the distances today. I performed the air tests today in my backyard, where I could run the AT Max at full sensitivity. And what a difference it did make.
The above pic shows the depth (in inches) for the shown targets. I was using the true all metal mode, with the iron audio turned off. It is by far the deepest mode, and should be used when searching for known deep targets and areas not too trashy. It is also the preferred mode searching for those tiny nuggets, easily missed by other metal detectors.
http://u.cubeupload.com/johnedmonton/237ATMaxFullSensitivity.jpg
Here is an air test using the zero discriminate mode. Again, it was set up using a threshold set at +2, noting soft whispers or a change in audio using the audio threshold. These again were the measurements that were used. Although not as deep as the true all metal mode, it still maintains a very good depth. And don't forget, that the AT Series have some of the best tones to ID targets correctly.
http://u.cubeupload.com/johnedmonton/d6eATMAXItemstestedGRAP.jpg
Here is a histogram comparison graph showing the differences in depth. It's all a mater of how a user utilizes his metal detector. On the one hand, a user can metal detect, hear those obvious good target ID sounding items and cherry pick the easy ones. However, those looking for those rare, well sought after targets will take advantage of the new Garrett AT Max's ability to sniff those extremely deep targets, often times missed by others.
Below is a pic of my air test target set up to pull out those numbers today. Remember, the air tests show a targets maximum potential. Depths will very from location to location. If a target has been in the ground for a very long time, part of it's surface may have broken down, leaching into the soil around it. The detector coil may read this as a larger target, allowing it to penetrate even deeper. To maintain a high level of reliability, I wore no watch, rings, belt and emptied my pockets. All targets were observed several times to make sure that the most accuracy was maintained for measuring repeatable audio at proper depth.
Unless the machine could identify it as a pristine 1916D mercury 
I mean a whisper of a signal at 17" on a dime in all-metal with no accurate VDI? Its impressive! However, I would not even take the time to see what it is. To me there is a cut-off on depth. To me, 10" on a dime with accurate VDI is deep enough on turf. IF I am someplace like the beach, then it is gloves off 
Like you Jim, I have had a ball with my AT Pro as well. Now, I am just waiting for the delivery truck to arrive 
I have to say that CZ-21 must be running on steroids. Hang on to that machine!