Regardless, try explaining a rainbow in the sky.
The idea that there is a link or correspondence between music and colour is a very old and very persistent one. According to McClain’s (1978) analysis, Plato linked the major second and perfect fifth to yellow and the perfect fourth to red, in an extension of the Pythagorean harmony of the spheres to encompass planets, tones and colours. Aristotle (1984) suggested a parallel between the harmony of colours and the harmony of musical intervals. Newton (1730/1952), when investigating the spectrum of light, linked the intervals tone, minor third, fourth, fifth, major sixth, minor seventh and octave to the colours red, orange, yellow, green, blue, indigo and violet.
In additive colour mixing (mixing coloured lights) the primary colours are red, green and blue. They combine according to the following rules: red and green make yellow, and yellow and blue make white (or grey, depending on the brightness). Similarly a major third and a minor third make a fifth, and a fifth and a fourth make an octave. (Other musical intervals can be regarded as compounds of these primaries. For example, a major seventh is a compound of a perfect fifth and a major third, and a minor sixth is a compound of a perfect fourth and a minor third.) These rules can be represented by tree structures.
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One of the basic elements of music is called color, or timbre (pronounced "TAM-ber"). Timbre describes all of the aspects of a musical sound that do not have anything to do with the sound's pitch, loudness, or length. In other words, if a flute plays a note, and then an oboe plays the same note, for the same length of time, at the same loudness, you can still easily distinguish between the two sounds, because a flute sounds different from an oboe. This difference is in the timbre of the sounds.
Timbre is caused by the fact that each note from a musical instrument is a complex wave containing more than one frequency. For instruments that produce notes with a clear and specific pitch, the frequencies involved are part of a harmonic series. For other instruments (such as drums), the sound wave may have an even greater variety of frequencies. We hear each mixture of frequencies not as separate sounds, but as the color of the sound. Small differences in the balance of the frequencies - how many you can hear, their relationship to the fundamental pitch, and how loud they are compared to each other - create the many different musical colors.
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