This app was mentioned in 13 comments, with an average of 3.15 upvotes
If you use Android, there's the bullion test app that uses your phones microphone to check the frequency when you ring the coin.
Bullion Test
https://play.google.com/store/apps/details?id=se.brolinembedded.bulliontestfree
I'm very impressed that it can distinguish between coins so consistently. It will test only a couple coins until you buy the full version. I won't even bother listing all the coins the full version will test (it's a lot and everything worth testing). It has several gold coins too.
The frequencies (timbre) are what matters for ping, which is testing the speed of sound in the material. Bullion Test for Android has a useful spectral display that shows the peaks (choose any coin, as you'll be ignoring its expected frequencies shown in blue). Perform it on one of the good coins, note the frequencies, then compare with the questionable coin.
You also need a pair of calipers (you can get digital for $10 on Amazon) to measure the diameter of your rounds and coins. It has many famous coins already programmed like ASE.
https://play.google.com/store/apps/details?id=se.brolinembedded.bulliontestfree&hl=en
Simpler, and just as reliable I would say, in todays market. Bonus points: It also validates older coins without the engraving.
I use the paid version of this free app when at flea markets. I think the US eagle is on the free version.
https://play.google.com/store/apps/details?id=se.brolinembedded.bulliontestfree
https://play.google.com/store/apps/details?id=se.brolinembedded.bulliontestfree I used this you can check American silver eagles and Buffalo coins free there is a paid version that let's you check a lot more here is that one https://play.google.com/store/apps/details?id=se.brolinembedded.bulliontest it's like 5 dollars. Keep in mind they make fakes out of copper so they are not magnetic. Although the rare earth magnet is the one you want to use. There is a good test so find real silver all you need is water a container and an accurate scale here is that method https://youtu.be/ES7u-F29rqM
Try using this app and see what the results say: https://play.google.com/store/apps/details?id=se.brolinembedded.bulliontestfree&hl=en
You can be deaf and still do a ping test using the Bullion Test Android app.
Ring the coin and test with the "Bullion test android app":
https://play.google.com/store/apps/details?id=se.brolinembedded.bulliontestfree&hl=en
Bullion Test Free. It doesn't have a lot of coins, but is pretty accurate.
https://play.google.com/store/apps/details?id=se.brolinembedded.bulliontestfree
Looks good to me, looks like it's toning. But find out with that free phone app:
https://play.google.com/store/apps/details?id=se.brolinembedded.bulliontestfree&hl=en