Mrs. Woodward and I love this video. Charmaine Brown does an amazing job of explaining chest voice, head voice, and that special place in between that we like to call mixed voice but she refers to it as pharyngeal singing. She also describes how important vowels are to shape your sound. When a choir can agree on their vowels they will sound AMAZING.
Riffs (often called runs) are basically an extension of a word with an embellished melody.
-This technique is only appropriate for solo singing & should not be used when singing with a choir.
-When done correctly, this can be an impressive display of vocal ability, but it should be used sparingly and most signers do not do it with complete accuracy.
In this video Natalie Weiss discusses how to break down and accurately learn a difficult riff.