Class A - you can hear what is being said with no aid

 Class B - you can hear most of what is said with earphones

 Class C - some kind of sound but cannot be made out.

 

We have 2- DR60 Panasonic recorders that are the bomb. They  stopped making them because  people kept picking up voices on them and they thougth it was a defect.

We also use sony, and olympus recorders.