EDWARD'S LECTURE NOTES:
More notes at http://tanguay.info/learntracker
C O U R S E
The Biology of Music
Dale Purves, Duke University
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C O U R S E L E C T U R E Tones versus Noise Notes taken on January 26, 2016 by Edward Tanguay |
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categories of sound signals
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we transduce sound signals using the machinery of the human auditory system
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two extremes
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tonal sound signals
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white noise sound signals
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tonal sound signals
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a sound that repeats systematically and continuously over time
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tuning forks are not natural sources of sounds
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you aren't going to find anything in nature that produces a sine wave
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harmonic series
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much more relevant to biology and music in particular
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e.g. a plucked string
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you can analyze that time varying signal of a plucked string by looking at its sound spectrum
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look at the sound spectrum
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a snapshot of the energy that this generated by the plucked string in a brief window of time
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the same thing happens to columns of air in wind instruments
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string 1:
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fixed at both ends
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when plucked, generates modes of vibrations
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these disturb the local atmosphere
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it vibrates at
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full length
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half length
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third length
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fourth length
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and so on
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because of the nature of the wave form
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when you take a snapshot, you get a spectrum described as a harmonic series
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the natural source of a tonal sound, generated by e.g. a plucked string, a column of air and the reed that disturbs it
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fundamental frequency
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the vibration that corresponds to the full length of the string
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the vibration that exerts the greatest disturbance to the atmosphere
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the first vibratory mode of a string or column of air
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the defining freqency of music or vocal tone, or any tone that is being generated in which there are vibrations of a series of modes
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the vibration at half the length
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the second harmonic
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the harmonics go on as long as you want to consider them
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tuning fork
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only generates a single frequency
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no harmonic series as with the a string
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tuning forks don't exist in the natural environment
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plucked strings and columns of air that produce a harmonic series are also rare in the environment
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almost always indicative of animals including humans and their way of communicating with each other
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most natural sounds are noisy
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the extremes in the range of human hearing
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1. sine wave and natural tones
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e.g. animal communication
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systematically repeating at a certain frequency
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2. white noise
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all frequencies equally distributed
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e.g. TV or radio static, or water rushing
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most sounds are between these two extremes
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the absence of a systematic repetition characteristic of a sine wave