Acapella is a form of singing that uses nothing but the human voice to
produce the sounds involved. This means that for a performance to be
called acapella, it has to be entirely based on the natural human voice
without incorporating instruments or backing music. The term a cappella
was originally intended to differentiate between Renaissance polyphony
and Baroque concertato musical styles. In the 19th century, a renewed
interest in Renaissance polyphony coupled with an ignorance of the fact
that vocal parts were often doubled by instrumentalists led to the term
coming to mean unaccompanied vocal music.
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