GPX series - Gain, motion, audio and stabiliser settings.

GAIN

From my perspective the gain setting is basically a sensitivity control. The manual tells us;

With a high Rx Gain setting the detector will pick up smaller and deeper targets, but may respond to unwanted interference and ground noise. A high Rx Gain setting is recommended for mild soil conditions and areas of low interference.

I use the gain as part of making sure the detector runs as smoothly as possible using conservative settings. Depending on the coil size, motion and audio filters chosen, I will run the gain between 8 and 20.

• If I use deep audio and a large mono coil in my area, I will select very slow motion, a gain of 8 to 10 and a stabiliser of 7 to 10 generally.
• If I select normal audio and a 14” round mono, I will select a gain of 10 and a stabiliser of 10 coupled with slow motion.
• If I select Quiet audio because the EMI is bad, then I will use very slow motion and a gain of 14 to 20 and a stabiliser of 15 to 20.I have run in quiet audio with gain and stabiliser both at 20 using a 14” NF mono coil and had the detector run well enough to pick out the sub-grammers with ease, whereas the more conventional settings as listed for normal audio above were fluttery at best.

And also from the manual;

Note: Be prepared to reduce the Rx Gain setting if the background threshold is erratic. A smooth threshold is preferred, as a lot of noise will drown out a soft target signal.

STABILISER

From the manual;

The Stabilizer function controls the point at which faint variations in the Threshold begin to be heard. These faint variations can either be ambient noise or faint target signals.

I often see detectors set at high gains, high target volume levels, medium or fast motion settings and a gain of 1. It beats me why some feel the need to crank the machine up using those selections and then have to resort to a low stabiliser to get the detector to run well enough to use. The stabiliser controls the spot at which faint variations are heard, so when we start to get the coil further from the target the response gets fainter. There comes a point where the selected setting is higher than the response from the target, so it will be missed entirely. As the stabiliser setting is lowered, the point at which a target is lost is at a spot closer and closer to coil.

If you have a target and approach it using a mono coil for example, you will get a response as the coil approaches even though it isn’t over the target, and all the way through until a spot where the coil is leaving or has left the target. As we lower the stabiliser setting it becomes apparent that the coil needs to be more over the target before a response is heard, until as we continue to lower the setting, the response may only be when the coil is centred on the target, or the response can be lost entirely (or missed for that matter if we have a low setting).

MOTION

From the manual;

The speed at which you sweep the coil has an effect on target response time and Ground Balance adjustment. Matching your preferred coil sweep speed with the corresponding Motion Setting can reduce noise and improve target signal responses.

Very Slow and Slow

This Motion setting provides a stable threshold, making it ideal for beginners and most detecting situations. When carefully detecting a small area, a Slow Motion setting will ensure good depth and sensitivity. For maximum performance, a slow and steady coil sweep needs to be employed when using the Slow Motion setting.

Note: It is quite important that the Motion setting you select matches the speed at which you swing the coil.

Medium

This Motion setting will often improve performance if a more moderate sweep speed is used. Background noise may increase just slightly compared to the Slow setting, so it is ideal for the more experienced operator.

Fast (GPX 5000)

Fast Motion is useful when using a fast sweep speed to cover ground quickly. In these circumstances, a quick sharp target response will alert the operator to a target. Fast will allow you to cover more ground in a shorter amount of time.

Note: The Motion speed also effects how susceptible the detector is to external interference. Basically, the slower the Motion speed the less interference you will get; resulting in a smoother Threshold. If the Threshold is too unstable while you are using Medium orFast Motion, you can select Quiet Audio Type (p. 64) or reduce the Rx Gain.

From that most people ascertain that if you have a fast swing speed then you use a fast motion and vice versa. I am going to stick my neck out here and disagree.

What happens when we swing over a target using a constant swing speed (doesn’t really matter what speed but say a conservative speed between fast and slow)? When we do and use the very slow motion the response is broader, slow motion is not so broad, medium is quicker and fast has the quickest and sharpest response. So the motion settings have a bearing on the target and the fast motion gives a fast response.

Now if we have a fast swing speed (and I do) the response is rapid as well. When I use a very slow motion setting it gives me a better response as the signal is not so short, where a fast motion makes the signal so quick that I believe it would be easy to miss some targets in the case of very small nuggets, or dismiss them as a “spike” from EMI. Conversely if I had a slow swing speed and used the recommended slow or very slow motion the target broadens and sounds to me more like a ground noise than a metallic response.

AUDIO

Again from the manual;

Quiet

This setting gives the most reduction of both ground noise and interference. The signal response is slightly quieter compared to the other Audio Types. Quiet should only be used in the most extreme situations.

Normal

This is the most versatile setting and should be used for general detecting conditions. Normal provides the best compromise for signal response and Threshold stability.

Deep

This setting is the preferred Audio Type when searching for larger targets at depth. It works well in combination with the Slow Motion setting, where target signals are distinct, but noise from the ground and electrical interference are somewhat filtered out.

Boost (GPX 5000)

This is a more aggressive Audio Type. Boost will provide very sharp target signals but will also increase any signal caused by ground noises or electrical interference. It is best used in milder soils and well away from electrical interference.

Note: Each Audio Type will have a different optimum Rx Gain setting so you should check the level of Rx Gain if you make changes to Audio Type.

This setting also has a large bearing directly on the amount of EMI you will experience if the environment is noisy. The deep setting (as opposed to Deep mode which is a name for a detector mode) will give a boost to the deeper targets as it suggests by name, boost is used for small coils and smaller targets and is excellent in conjunction with the Fine Gold timing, normal has no boost or enhancements and is a good all round setting, while quiet is excellent at reducing the EMI present.

Using quiet audio alone may result in some performance loss, which can be regained by increasing the gain and stabiliser levels quite high. The table at the end of this document has settings that I revolve around for my detector in the 3 easily accessed modes. If you have a target and try each of those modes on it, for the most part you will find that the custom mode (Patch is the name unless it was changed) will give the best and loudest response.

There is a method of using a detector called “Bogene’s Settings” after the gent who came up with them. They are to basically turn the threshold down to nothing (right off) and turn the sensitivity (gain) and stabiliser up full. The detector will run pretty much dead quiet and the target signals will jump out. This method can be used on the GPZ7000 by using whichever gold mode and ground type suits the area being detected, turning the threshold to 1, audio smoothing off, and the sensitivity to 20. If the environment is noisy for whatever reason, this method will allow you to detect and still find gold where you may have had to go home, or find another spot.

CONCLUSION

Be prepared to experiment as there is more than one way to “skin a cat”. There probably isn’t a “right” way, but there can be lots of “wrong” ways. If you use more conservative settings to get your detector running smoothly, then that is preferable in my book to using some of the more radical settings that I see and am told about. On a last note, if the settings you are using seem to work for you, then by all means use them, but be prepared to consider other alternatives when necessary.