A double reed is a type of reed used to produce sound in various wind
instruments. In contrast with a single reed instrument, where the
instrument is played by channeling air against one piece of cane which
vibrates against the mouthpiece and creates a sound, a double reed
features two pieces of cane vibrating against each other. The
term double reeds can also refer collectively to the class
of instruments which use double reeds. The timbre of a single reed
instrument is related to the harmonic series, while the timbre of a
double reed instrument includes only the odd harmonics since the two
reeds alternately touch each other and separate while vibrating, thus
canceling out the even harmonics, and this may be compared to the timbre
of a square wave.
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