Acoustic Waveforms Acoustic Waveforms Simple Harmonic Motion ...

Waveforms and Damping (8)
• Note that it is common to refer to both a
sound and the system that generates it as
possessing some relative degree of
damping.
Adding Waveforms & Phase (2)
Here we can see the effect
of adding two pure tones,
one of 100 Hz and the other
of 500 Hz. The 500 Hz tone
has half the sound pressure
level of the 100 Hz tone. In
the bottom part of the
diagram we can see the
two pure tones as dashed
lines. A simple addition of
the dashed lines results in
the unbroken line. The
unbroken line clearly has a
more complex pattern than
either of the two pure tones.
Adding Waveforms & Phase (4)
• In the next slide we add together three
waveforms with frequencies of 100, 200
and 300 Hz. (Highest common factor 100)
• They differ in the positions of the start of
each wave cycle.
• In the left image they all start at 0°.
• In the right image they start at 0°, 90° and
180° (going from the lowest to highest
frequency)
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Adding Waveforms & Phase (1)
• So far, we have examined simple
waveforms that resemble sine waves.
When we plot a pure tone we can easily
see its period (or frequency) and
amplitude (sound pressure level).
• The vast majority of natural sounds are not
pure tones but are complex sounds that
can be thought of as the combination of
two or more pure tones.
Adding Waveforms & Phase (3)
• Note, in the previous slide, that the complex
pattern repeats with the same period as the
100 Hz tone.
• 100 Hz is the highest common integer factor of the
frequencies of the two tones (100 and 500 can
both be divided by 100 to give an integer result).
• The frequency of a complex wave is always equal
to the frequency of the highest common factor of
the sine waves being added to produce it.
• The repetition frequency of the complex pattern is
called its fundamental frequency (F 0).
Adding Waveforms & Phase (5)
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