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Semitone scale

PHONETICS: Twelve semitones form one octave, which is defined as a doubling of the fundamental frequency. As the human auditory system perceives tones in a logarithmic way (instead of in a linear way), the logarithmic semitone scale is a more appropriate measure of the perceptual consequences of differences in fundamental frequency. The following conversion transforms frequency (F) values into semitones (ST):
ST=39.87*log(F/50)