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WAVELENGTH AND MUSICAL PITCH


Guitar strings vibrate along a particular distance.  At half the distance (12th fret) it vibrates at twice the frequency (1 octave).  Western music is based on set divisions of notes, and combinations of those set divisions.  The combinations will produce predictable sound combinations that can elicit specific emotions.  For example, a Major key sounds “happy” while a Minor key sounds “sad”.  Non-western music often uses notes that are IN BETWEEN the western divisions.  As a result, there are emotions that can be expressed in non-western music that are not found within western music (since they use note combinations that include notes that would be found in between white and black piano keys).

Sound waves need space to develop.  A fast, high frequency sound wave may finish one complete cycle in a short distance while a slow low frequency may need several feet or yards.

When a sound source is moving towards you, the sound waves are squeezed closer together.  This makes the sound waves appear higher in pitch.  When a sound source is moving away from you, the sound waves are pushed further apart and appear lower in pitch.  If the sound source approaches, passes then moves away from you it will sound as if the sound is getting higher in pitch until it passes you and gets lower in pitch.  Imagine a motorcycle speeding towards you, passing and then speeding away.  This is called the DOPPLER SHIFT.

A good way to understand the Doppler Shift is to consider someone throwing a rock at you every 2 seconds from far away.  If he starts to run very fast towards you and still throws every 2 seconds, the rocks that he throws when he is closer to you have less of a distance to travel and so need less time to get to you. This will make it seem like the rocks are being thrown more frequently.  The speed of the rocks being thrown has not changed, but they arrive at you in shorter amounts of time as long as the thrower is still running towards you.

This is the same as sound waves from an approaching source seeming to arrive faster, with a faster frequency and high musical pitch.

When the thrower runs away from you still throwing a rock every 2 seconds, since he will now be throwing from increasing distances from you the rocks will take longer to arrive to you, which will make their frequency seem more than 2 seconds apart.  Again, the speed with which the rocks are being thrown has not changed, but you perceive them as arriving slower due to the increased time required for the rocks thrown further to cover the extra distance.

This is the same as sound waves from a departing source seeming to arrive slower, with a slower frequency and lower musical pitch.

The Doppler Shift is usually heard when something is coming towards you, passes, and then travels away from you, creating the impression that the sound it makes is rising in musical pitch until it passes you and then the musical pitch drops downward.