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Music Theory  Frequency and pitchTo develop a good understanding of how music works it is necessary to start with the basics of sound, pitches and notes. Frequency and Vibration In terms of pitch big means low and small means high. If you strike two metal rods of equal thickness but differing lengths the longer one will produce the lowest note. This is true whether the vibration is in a metal rod, a string or a column of air. Pitch In music, however, there are a finite number of pitches. How then do we make the transition from frequencies into musical pitches? To some extent the relationship between the note pitches of Western Music and the natural frequencies of sound is arbitrary in the sense that there are other ways of doing it. There are good reasons for the chosen relationship, however, and these are outlined below. The most obvious limit to impose on the infinite frequencies of nature is that of mortal hearing. There is little point incorporating pitches into a musical system if they are above or below our hearing spectrum. The Octave The second logical organisation of natural pitches rests on a phenomenon known as the octave. This is a naturally occurring law that means that if you double the frequency of a note you will get a note that sounds the same only higher. Thus if we pick a frequency of 110Hz and call it "Note A" we will find that 220Hz gives another, higher A as does 440Hz etc. Using our analogy of metal rods again a rod twice the length of another should produce the same note but an octave lower. We now have a very simple basis for mapping out frequencies in terms of musical pitch: DIAGRAM OF OCTAVE Below Human HearingAbove Human Hearing Splitting the Octave into Musical Intervals Clearly a tune with only one note (even with high and low versions) would be pretty dull. To create a usable set of musical pitches it is necessary to subdivide the octave. While the octave is common to all cultures different musical systems have differing approcahes when it comes to dividing it up. The octave and its subdivisions are known as musical intervals. Diagram Of Harmonic Series Western music splits the octave into 7 basic notes and calls them by the letters of the alphabet. A B C D E F G The spliting, like the octave, is based on frequency ratios. Simple frequency ratios produce consonant (or pleasing) intervals and more complex ratios (with closer frequencies) produce dissonant(less pleasing) sounds. The different intervals and their frequency ratios are outlined below: 1:1 Unison (two of the same note) Imperfect consonances: 4:5 Major Third Dissonances: 8:9 Major Second (Tone)  
