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St Catherine’s News Autumn 2020
Psychoacoustics
& THE HARMONIC SERIES
Before music hits our ears it exists in the air as an intricate series of pressure waves. What is fascinating is the incredibly complex decoding that our brains perform in order to perceive this jumble as music. Simply being able to recognise an instrument from its tone (timbre) requires incredible computing power.
HARMONIC SERIES How is it that most of us can instantly distinguish whether we are listening to a trombone or a violin even if they are playing simultaneously, or buried deep within a symphony orchestra? When any physical instrument (not a synthesizer) ‘plays a note’, it also generates a number of other notes. When a trombone plays an ‘A’ at 220 Hertz, it also produces the note ‘A’ (440Hz) an octave above, the ‘E’ (660Hz) above that, the ‘A’ (880Hz) above that, then C# (1.1kHz), E (1.32kHz), G (1.54kz), A again (1.76kHz), B, C, C#.
This pattern continues ad Infinium but the frequencies get so close together that they no longer correlate notes on the piano. This is the harmonic series and was well known to Pythagoras in the 6th Century BCE. The harmonic series occurs in nature and contains within it a pentatonic scale (A, C#, D, E, G, A in the above example). Possibly, this is why most cultures share the pentatonic scale as the basis of their traditional melodies. All of our students in Year 8 will be familiar with the pentatonic scale as it forms the basis of our aural training in Years 7 and 8. The harmonic series is the reason the bugle can play the Last Past without any valves at all.
