Play a scale from E2 to E4. Take note of how easily the singer hits the lower notes. If the singer does not hit the majority of the lower notes, he may be a Baritone. If the singer can hit these notes, he is a bass.
Play a scale from F2 to F4. Take note of how easily the singer hits the lower notes. If the singer does not hit the majority of the lower notes, she may be a Tenor. If the singer easily hits all notes in this scale, then she is a Baritone.
Play a scale from C3 to C5. Take note of how easily the singer hits the high notes. If the singer comfortably sings all the notes within this scale, then he is a Tenor.
Play a scale from F3 to F5. Take note of how easily she sings the lower notes. If the vocalist easily sings them, then she is an Alto. If your singer has difficulty singing them, then your singer may be a Soprano.
Play a scale from C4 to C6. The singer easily should sing these notes if he is a Soprano. If the singer has trouble singing the higher notes, but he cannot sing the low notes of an Alto, then he is a Mezzo-Soprano or Middle Soprano.