https://www.youtube.com/watch?v=1umvRRm5Eg4
The viewing option shown at around 0:30 is very useful for seeing one or multiple voices simultaneously to check on and identify the source of tuning issues.
(I have no affiliation with whomever makes this app; it's just fascinating).
https://play.google.com/store/apps/deta ... c.pitchlab
Using PitchLab guitar tuner for voices
Re: Using PitchLab guitar tuner for voices
This app has come to semi-affectionately be referred to as the "bitch slap" application by choristers who don't love being told that they're the voice part or singer that's going flat.