
When the tuning, balance and a given word sound are properly executed, certain harmonics associated with the notes being sung are enhanced, while others are diminished, resulting in a fifth note that is audible two octaves or more above the four notes being sung. This phenomenon is known as an "overtone," and it is a vital ingredient of Barbershop Harmony when performed well.
There are other facets of barbershop harmony that are frequently used, but not always present in every performance. Frequent modulations (key-changes) within a song are facilitated by the true scale and the singers' ability to immediately "tune" their vocal instruments. "Bell-chords" are sometimes used to illustrate the four voice-parts, sometimes while also "painting" a word or phrase. Sliding during an interval (from one note to another) is a vocal technique that adds contrast and style.
While stereotypical elements of barbershop groups such as striped vests, handlebar moustaches, and straw hats remain; in reality, American Popular Songs are now performed by thousands of contemporary male and female barbershop ensembles comprised of singers who exhibit a wide range of racial, religious, and ethnic diversity, not only in the USA but in a dozen other countries throughout the world.