It wasn't the tuning. It was just that one note they sang. Ab#.
LOL
Well there are such things and quarter tones (between two notes) and microtones (between quarter tones) which are basically notes between notes. The note you heard is actually called "A quarter flat". To those who play western style music, it sounds out of tune, maybe a little flat or a little sharp but other cultures like Celtic, Eastern (chinese/japanese), and especially Indian have made complete scales out of these kind of notes. So in your situation, it means one of two things: your choir is off da hook because they can hear and sing quarter tones or you have a little tuning problem and all it takes are some pitch exercises to get everything back to normal. Considering that we're playing gospel though, I would say it's the latter, lol. Just have them tune to your piano but first make sure the piano is in tune. You can set to default settings or check with a tuner (like the ones your bass probably uses).
Actually it happens a lot when the choir or any wind instrument groups are listening to one another and tuning to each other. If one person sings/plays the pitch off slightly, everybody will tune with it and all be off; however, they're all still "in-tune" with each other just not with a piano. It's actually a very fascinating occurrence how people tune with their ears. I hope that made sense.
