steve herschbach
New member
OK, what do I mean when I talk about Target Resolution, VDI Spread and Target Stability?
Look at it this way. On Garrett Ace 150 you get 5 VDI readings which Garrett gives names (iron, nickel, pulltab, rings, and coins) but really should just 1, 2, 3, 4, and 5. All targets fall under one of these five VDI segments. Obviously, you get a huge amount of target overlap.
Go to the Ace 250, now you get 12 target segments. Now targets that read the same on the Ace 150 can give you a different reading on the 250.
Go to the Minelab X-Terra 505 and you get 19 target segments or VDI numbers. And the Minelab X-Terra 705 offers 28 target id possibilities.
The standard White's scheme runs from -95 to +95 so you have 190 possible target VDI numbers.
I refer to this whole idea of increasing target segments as "target resolution".
White's based their original scheme around the 6.59 kHz frequency. When you go to higher frequencies, the VDI numbers on the high end compress and the VDI numbers on the low end expand as the VDI range gets shifted higher. The reverse happens when you go to lower frequencies. So in order to not confuse people who have learned to relate certain items to certain numbers, White's usually "normalizes" the numbers by correcting for this in software.
So in 22.5 kHz mode if you turn normalization off, you get a wider spread between low conductor targets. High coin readings are more likely to lump together.
Gold falls all through the lower VDI range, so VDI is useless on gold per se. What VDI does is allow you to zero in on one particular pull tab that infests an area, for example. You can skip that tab if you choose. At least some gold items that read the same as the tab on the compressed normalized VDI will now spread far enough away from the tab to now be seen as a separate target. The more VDI spread you can get between targets, the less chance there is of misidentifying items.
In 2.5 kHz mode, turn off normalization and you have a better chance at being able to tell a copper penny from a silver dime.
What I call "target stability" is the apparent ability of a detector to "lock" onto a target. Using fewer target segments offers a false sense of security as a unit with few target segments is far more likely to solidly lock onto a target. The underlying reading may be jumping around, but as long as it falls into the broad range as defined by a system with few possible target segments you get a very consistent reading.
As target resolution increases you get an apparent decrease in target stability. Many people wonder why when using a White's that the numbers often "jump around". That is because reality is being revealed to you that is masked in other detectors. The speed, angle, and height with which you pass a coil over the target varies every time. On shallow targets the reading is strong enough to give you solid locks. But on very deep or tiny items the signal is weak enough that it will vary along with how you hit the target. If you could program a mechanical arm to move the coil for you no doubt you'd get more consistent readings. So experienced users learn consistent coil control and employ some mental "target averaging".
One fun thing about the V3 is you can set your own custom icon schemes to match custom VDI ranges, creating lower resolution VDI schemes if you wish. You can turn off the VDI numbers, create a "nickel" VDI range, and give it a nickel icon. This would increase the apparent ability of the unit to "lock" onto a target but the reality is you are just lumping a range of VDI responses into a single delivered result.
The same thing applies when you assign tones to VDI ranges. In the 256 "multi-tone" mode tones jump around. Set up a 12 tone scheme and you'll get very consistent tones. But less target resolution.
You can probably guess why I like playing around with the V3. It can be made to emulate many other types of detectors on the market. You can create an "Ace 150" program or an "X-Terra 70 program". And I'll bet we start seeing just that as people start playing around with the unit more.
Steve Herschbach
Look at it this way. On Garrett Ace 150 you get 5 VDI readings which Garrett gives names (iron, nickel, pulltab, rings, and coins) but really should just 1, 2, 3, 4, and 5. All targets fall under one of these five VDI segments. Obviously, you get a huge amount of target overlap.
Go to the Ace 250, now you get 12 target segments. Now targets that read the same on the Ace 150 can give you a different reading on the 250.
Go to the Minelab X-Terra 505 and you get 19 target segments or VDI numbers. And the Minelab X-Terra 705 offers 28 target id possibilities.
The standard White's scheme runs from -95 to +95 so you have 190 possible target VDI numbers.
I refer to this whole idea of increasing target segments as "target resolution".
White's based their original scheme around the 6.59 kHz frequency. When you go to higher frequencies, the VDI numbers on the high end compress and the VDI numbers on the low end expand as the VDI range gets shifted higher. The reverse happens when you go to lower frequencies. So in order to not confuse people who have learned to relate certain items to certain numbers, White's usually "normalizes" the numbers by correcting for this in software.
So in 22.5 kHz mode if you turn normalization off, you get a wider spread between low conductor targets. High coin readings are more likely to lump together.
Gold falls all through the lower VDI range, so VDI is useless on gold per se. What VDI does is allow you to zero in on one particular pull tab that infests an area, for example. You can skip that tab if you choose. At least some gold items that read the same as the tab on the compressed normalized VDI will now spread far enough away from the tab to now be seen as a separate target. The more VDI spread you can get between targets, the less chance there is of misidentifying items.
In 2.5 kHz mode, turn off normalization and you have a better chance at being able to tell a copper penny from a silver dime.
What I call "target stability" is the apparent ability of a detector to "lock" onto a target. Using fewer target segments offers a false sense of security as a unit with few target segments is far more likely to solidly lock onto a target. The underlying reading may be jumping around, but as long as it falls into the broad range as defined by a system with few possible target segments you get a very consistent reading.
As target resolution increases you get an apparent decrease in target stability. Many people wonder why when using a White's that the numbers often "jump around". That is because reality is being revealed to you that is masked in other detectors. The speed, angle, and height with which you pass a coil over the target varies every time. On shallow targets the reading is strong enough to give you solid locks. But on very deep or tiny items the signal is weak enough that it will vary along with how you hit the target. If you could program a mechanical arm to move the coil for you no doubt you'd get more consistent readings. So experienced users learn consistent coil control and employ some mental "target averaging".
One fun thing about the V3 is you can set your own custom icon schemes to match custom VDI ranges, creating lower resolution VDI schemes if you wish. You can turn off the VDI numbers, create a "nickel" VDI range, and give it a nickel icon. This would increase the apparent ability of the unit to "lock" onto a target but the reality is you are just lumping a range of VDI responses into a single delivered result.
The same thing applies when you assign tones to VDI ranges. In the 256 "multi-tone" mode tones jump around. Set up a 12 tone scheme and you'll get very consistent tones. But less target resolution.
You can probably guess why I like playing around with the V3. It can be made to emulate many other types of detectors on the market. You can create an "Ace 150" program or an "X-Terra 70 program". And I'll bet we start seeing just that as people start playing around with the unit more.
Steve Herschbach
