This expression is no longer just a way of describing good vocal projection. We are now wearing face coverings to sing in church choir, to forestall any objections that we might not be protecting our congregation sufficiently.
If I’m going to sing services in a mask, I’m going to have them in the full range of liturgical colours
I haven’t heard the results, though I’m told by those who have that our sound is still acceptable. There are some practical problems though. One is that we can’t ‘read the lips’ of our conductor for such matters as ends of words. Another is sucking in the material when you breathe in, though this happens less with the fairly thick material I’ve made masks from. I think that, erm, the length of one’s nose also makes a difference here.
I was worried about jaw tension creeping in and so far this hasn’t happened to me, although I haven’t yet had to sing anything with lots of high notes in. My main problem is that I don’t really associate what I hear with the effort I make to produce it. I can’t tell how consonants are coming over, what the tone is like, or how loud it sounds. With practice I might get better at judging this but the lack of physical engagement with the sound is disconcerting.