GPZ 7000 Threshold Setting Concerns

[jasong]

17 hours ago, Northeast said:

Somewhere in the deepest, darkest DP Forum threads JP mentions something like 'raising Volume by 1 notch is akin to raising the Sensitivity by 2'. 

I remember reading something along those lines too. When daybreak hits Australia if JP is around, I wonder if he might go into more depth there?

Like, it doesn't actually increase the TX or RX sensitivities right? It's still adjusting only the processed audio feed right? Or does the volume control on the GPZ actually have some tie to the actual sensitivity too?

[1515Art]

I’ve tried running the 7000 a number of different ways and will still make a second or third pass trying different setting over an area I’ve hit a nugget, but most of the time have my best success running it conservative. I’ll run the threshold at 27, sensitively around 8 to start depending on soil as low as 5 or high as conditions permit, high yield, normal ground, smoothing off and locate patch filter on with volume set to 6 or 8, g/b semi auto. These settings give me fairly quiet running yet still plenty of feedback on ground noise while sensitive to very small targets. This tiny gold basin meteorite is an example of the sensitivity at these settings found down a couple of inches. 

[Gold Catcher]

Chet, if you prefer a GPX5000 type smooth treshold, then use Lunk's settings for the 7000. That's as close as it can get.

[Lunk]

11 hours ago, Chet said:

Mitchel, Lunk was one of my trainers; I have tried his settings but his Threshold of 35 is just too noisy for me

Chet, I have since lowered my threshold to 27/28; it's not nearly as intense and the target responses are more distinct.

[Jonathan Porter]

A few things to get everyone on the same page settings wise between the 5000 and the 7000. Firstly the 5000 has a Stabilizer control that goes from 0 to 20 with Zero being the highest noise floor filtering (noise floor is raised to filter out a lot of target signals) and 20 where the noise floor is as its lowest point allowing basically everything through.

The GPZ has a control like this too called Audio Smoothing, when I see people complaining about more noise generally this is due to them being used to an extremely filtered environment with the 5000, out of the box the GPZ is set at Low Smoothing which is equivalent to running 15 on the 5000. There are not too many operators who are brave enough to handle 15 on the GPX because the threshold instability will drive them nuts. This is because the 5000 electronics are no-where near as refined as the GPZ so suffers a lot more from EMI, especially Sferic EMI (garbled variable noise).

The GPZ factory preset is far more aggressive than the 5000 due to that fact alone, as such the Volume (Target Volume equivalent of the 5000) and Threshold are all set differently to compliment the lower filtering the GPZ can handle. So you the operator have to search around a bit if you want to get the detector noise similar to what you are used to or give your brain a chance to “learn” the new way the detector behaves and soon enough you will not notice the busier baseline of the detectors audio. I always train new GPZ users with Audio Smoothing Off, it is much easier to go from Off to Low than it is the other way round.

The next thing in the GPZ’s favour is it’s balanced coils, nulled DD like coils have this neat trick of taming surface ground signals whilst maintaining good depth, in the case of the GPZ it requires a DOD style coil to avoid ‘movement signals’, this then means the GPZ is less reactionary to surface responses relative to the coil however it is different to say a GPX 5000 with a DD on because ZVT is a LOT more aggressive than MPS. 

On both the GPX 5000 and GPZ the ‘Target’ Volume (detect page menu bottom right on the GPZ) is extremely steppy in its behaviour (quite big movement in only one notch point past optimal), however its behaviour is impacted a lot of what the Stabilizer setting is or the Audio Smoothing setting position is, as such whatever you choose impacts on where the Volume ends up and also how you listen to the detector determines the volume position (headphones, WM12 speaker etc).

I always advise using the GPZ with Audio Smoothing OFF, this way you can easily adjust the threshold and volume controls to suit. I never use the Smoothing on any other position because I like to be coupled directly to the receiver information wise on the machine. The threshold setting of 27 was chosen to compliment the Audio Smoothing at Low and Off positions as such if you go to the High position (equivalent to the GPX 5000 FP Stabilizer setting of 10) then your volume and threshold settings will sound muted and hard to hear.

A good way to gauge the effect Audio Smoothing has on the GPZ and to get us all on the same page, using High Yield Difficult, put the Audio Smoothing in the OFF position, put Threshold on 27, put the Volume on 12, preferrably in a quiet environment, perform a noise cancel with the coil in air away from the ground and held flat, listen to the threshold and confirm it is reasonably stable.

Then bring the coil to the ground and go into Audio Smoothing settings, highlight High Smoothing (make sure you have the WM12 in a good position as if you were detecting, usually your swinging arm shoulder side), listen to and familiarise yourself to the volume of the detector behaviour (you can swing the coil side to side once ground balanced to get a feel for the way the machine sounds), then select and confirm High Audio Smoothing and notice the immediate dulling and volume lowering of the threshold, there is also a corresponding nulling of ground signals and target signals as well. To then get your machine back to sounding like it did with Smoothing on OFF you need to adjust the volume and threshold levels to suit.The difference between Off and Low is less profound but still relative so once again you will need to make adjustments to get things back on an even keel.

There is another thing about the GPZ that needs to be taken into consideration, the difference between Normal and Difficult is quite profound, Normal has incredible depth because the timings are fully opened up and you’re just relying on ZVT to deal with ground signals (does an amazing job compared to a VLF), the Normal Timings are far more aggressive and as such have a lot more headroom for filtering ect. 

I think this is where I have come unstuck with my American cousins when it comes to Audio Smoothing because the ground they are working allows for the use of Normal with elevated sensitivity. 🥴 Normal has a much busier volume associated with the timings as such you will need to tweak the threshold and volumes dependant on your ground type. There is plenty of headroom to compensate for timing variability by using the Audio Smoothing as a control rather than going to the extreme of using Difficult.

Difficult kills depth right across the board relative to ground signal so it is always better to use Normal wherever possible. Difficult does have very good sensitivity to small close to coil targets and it also presents much better on 12 to 20 gram pieces at edge of detection depths (this is the same as the 5000 too), so it will pay to go over ground again using HY Diff with the Sensitivity cranked and Audio Smoothing Off just in case there are a few nuggets in that size range that has been missed due to the ‘hole’ in the timings, just make sure you give yourself at least an hour to relearn the way the threshold sounds compared to Normal as it can sound a lot different (Difficult has a lot of Gain built into the timings to lift the faint signals so can sound a bit twitchy when you go to them after using Normal a lot).

I hope this goes some way to explaining things.

JP

[Chet]

Jonathan

What outstanding information!

Minelab should hire you to rewrite their manuals!

Good manuals sell products.

I will take this information to the field and put it to work. 

Thank you and have a great day,
Chet

 

[Jin]

JP, that article must have taken some time to write, so thank you.

[Gold Catcher]

1 hour ago, Jonathan Porter said:

Normal has a much busier volume associated with the timings as such you will need to tweak the threshold and volumes dependant on your ground type. There is plenty of headroom to compensate for timing variability by using the Audio Smoothing as a control rather than going to the extreme of using Difficult.

Thanks, JP, another outstanding write up! Just to clarify, in cases where switching from normal/smoothing-off to difficult/smoothing-off is considered, you would try normal/smoothing-on first?

Thanks

 

[Steve Herschbach]

JP da man! 👍🏼

[flakmagnet]

That is the clearest most understandable explanation of those controls I have ever come across. It took careful thought to set out and probably quite a bit of time. Thank you.