RPE 1-2:

Very easy; you can converse with no effort

RPE 3:

Easy; you can converse with almost no effort

RPE 4:

Moderately easy; you can converse comfortably with little effort

RPE 5:

Moderate; conversation requires some effort

RPE 6:

Moderately hard; conversation requires quite a bit of effort

RPE 7:

Difficult; conversation requires a lot of effort

RPE 8:

Very difficult; conversation requires maximum effort

RPE 9-10:

Peak effort; no-talking zone