The TDI has no discrimination abilities and is an all metal machine. However, you can use the Target Conductivity control to identify targets by their conductivity properties.
The control allows you to select whether you want to hear only low conductive targets, only high-conductive targets, or both low and high conductive targets. Low-conductive targets, like small-to-medium sized gold nuggets will make a high-tone sound. High-conductive targets like coins, except nickels, will make a low-tone sound.
You would set it to low for low-conductive metals only, which would includes small to medium-sized gold nuggets, most small to large specimen gold in quartz, small gold rings, very small silver rings and small gold coins, nickels, small thin hammered silver coins, small bronze Roman coins, small boot tacks, lead bird shot, tiny broken bits of iron, aluminum pull tabs, foil and bits and tips of small nails, etc.
You would set it to high for high-conductive metals only, which includes all U.S.coins (except nickels), most silver rings, silver U.S. coins, very large gold rings, large gold nuggets, very high content gold nuggets, U.S. gold coins above 2.5 dollars, 24 K gold bullion, small to large nails when laying flat in the ground and large pieces of iron, large pieces of lead, lead mini balls, lead musket balls, lead loom weights, bronze buckles, bronze weights, bronze artifacts, etc.
When prospecting for gold, it is possible to reject a large nugget when selecting to only hear low-conductive metals. The size where a nugget can be classified as large is not exact as its shape and configuration can also be a factor. However, most all small-to-medium sized gold nuggets will fall in the low-conductive category. If the gold in the area being searched is predominately small to medium sized, then searching in low conductivity only will find most gold, and eliminate most iron trash.
Coin hunters can avoid digging pull tabs, foil and small bits of iron trash by using high conductive only.