Nah, it's not the new machines. I'm still finding old silver in the same parks with the same machine I've been using since the mid 90's.
In fact, I just went to an old park last week and found silver.
I noticed that the park was getting more quieter and therefore dug the signals that no one wanted to dig.
One such signal was iffy and after I removed two bottle caps, there was a nice faint "zing" signal underneath, which turned out to be a 1903 dime at around 8 inches deep. I also found several old coppers that actually discriminated out.
Because it's the wrong time of year for relic hunting and I had nothing better to do, I continued to dig all the faint discriminating signals and came home with a handful of old rings, brooches, pins, buttons, and other old knick-knacks.
There were even plugs everywhere from some new reality show treasure hunter wannabee.
Sure, you could buy a whole arsenal of detectors to give you "The edge" or you can just change your mindset and take a risk and dig more iffy signals.
Better yet, quit going to the same old parks that everyone and their dog goes to (and has gone to for 50 years) and try getting permission to hunt a virgin site.
You don't dig, you don't get.
Cheers,
Dave.