A signal instrument is a musical instrument which is not only used for music as such, but also fit to give sound signals as a form of auditive communication, usually in the open air. Signal instruments are often contrasted with melodic and diatonic or chromatic instruments ("a musical (rather than signal) instrument" is not uncommon phrasing). To make the message audible at a distance, percussion and brass instruments, which are generally loud, are chiefly used for this purpose. There are contemporary instruments which evolved from signal instruments, such as the natural horn evolving to the trumpet.
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