Because I sing a cappella from time to time, I know that the skill involves more than just the ability to sight-read: perhaps more than in any other genre of music-making one must be able to do so and listen at the same time.  Otherwise one can sing the right notes and be out of tune at the same time.
The difference is overtones: Overtones are brought into play by two sometimes separate, sometimes unified elements: consonant intervals and vowel matching.  A fine musician listens for consonant intervals which, in Renaissance counterpoint (like the Vittoria mass I heard this morning) are almost always somewhere to be heard, and for vowels matched by another voice, a function of the text setting.  
Unfortunately, the voices that must be most sensitive to these factors are the top voices, soprano, tenor.  If they don't recognize the occasional need to let resonance take over they sound simply shrill and out of tune. 


Comments are closed.