A cappella - Wikipedia
en.wikipedia.org
Although a cappella is technically defined as singing without instrumental accompaniment, some groups use their voices to emulate instruments; others are more traditional and focus on harmonizing. A cappella styles range from gospel music to contemporary to barbershop quartets and choruses.
A CAPPELLA Definition & Meaning - Merriam-Webster
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Because no independent instrumental parts were written down, scholars once thought that the choir sang unaccompanied, but current evidence makes clear that an organ or other instruments doubled some or several of the vocal parts. Regardless, today a cappella describes a purely vocal performance.
A cappella - Wikiwand
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Music performed a cappella, less commonly spelled a capella in English, is music performed by a singer or a singing group without instrumental accompaniment. The term a cappella was originally intended to differentiate between Renaissance polyphonic and Baroque concertato musical styles.
A Cappella Singing Techniques - Musical Mum
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A cappella singing, an art of unaccompanied vocals, emphasizes harmony, rhythm, and dynamics for a rich sound. It requires mastering voice control, harmonizing, and often mimicking instruments to enhance song arrangements.