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