Frequency
is a complex subject and it is usually worked out by the length of a
sound wave and how many times that oscillates or vibrates a second,
another name given to this is Hertz, for example if a stringed
instrument is plucked or scraped and vibrates 440 times a second it
is perceived as the note of A, if it vibrates 330 times a second it
is perceived as the note of E, this is what determines this
instrument to be pitched.
Pitch
is the name given to different types of frequencies, the most
common we use is the twelve keys on an octave, C, D, E, and so on. On
a guitar the string has to have tension to produce a pitch but the
shorting of a string on the fret board creates a higher pitched sound
and the longer the string on a fret board the lower the pitched
sound. The main factors of a pitched string are the tension, length
and mass. This chart shows the pitches related to their
frequencies.
Sound
waves
are moving energy or a vibration in the air that travels in waves
that disturbs the air pressure, as the sound travels it slowly loses
its energy. The air around us is made up of small particles that are
known as air molecules. To take a reading of how many molecules are
in the air we use a device called a Barometer this checks the change
of air pressure and is measured in decibels. Air pressure is
measured on how many molecules are in the air. The lower the
molecules are the lower the air pressure.
This
is a diagram of a sound wave and how it disturbs the air pressure.
To
give more detail on this diagram the energy from the source pushes
the air molecules forward and compresses them together, they then
expand back to there original source size.
There are three main factors of a sound wave. This sound wave is
called a sine wave.
Wavelength determines the length of the wave Amplitude determines the loudness or strength of a wave Frequency determines how many times this happens a second
The
first of these pitched sound waves to occur are also called the
fundamental, but as they travel through the air and lose their energy
there are higher pitches occurring above the fundamental these are
called the harmonics or overtones.
Harmonics
are
only generated by the fundamental that divides the length into
smaller sound waves, these sound waves or divided into equal arranged
parts of two three four five six seven and so on till the sound wave
completely loses its energy. With each divided part following, the
next one will sound higher in pitch but lower in amplitude. These
series of events are called The Harmonic Series.
The diagram below gives a better visual understanding.
Enharmonic
tones can also occur after the initial attack of the fundamental as
well but these overtones don’t belong to the harmonic series but
are said to be the neighbouring tones of the harmonic ones in other
words very close to being harmonic. Many percussion instruments
create enharmonic overtones, like Crash cymbals and Hi-hats, but
string instrument are less enharmonic because the strings are
stretched to prevent this. Partials is another name given to these
overtones but also can be referred to both
Transient
Partials
is another set of overtones that occur at the attack of the
fundamental overtone but diminish very quickly, on a guitar string
this is caused by the scrape of the plectrum on the string, on a
violin its much more noticeable because the bow is constantly
scraping on strings, transient partials vary in sound with different
players of the same instrument.
