Acoustic Waveforms Acoustic Waveforms Simple Harmonic Motion ...
Acoustic Waveforms Acoustic Waveforms Simple Harmonic Motion ...
Acoustic Waveforms Acoustic Waveforms Simple Harmonic Motion ...
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Adding <strong>Waveforms</strong> & Phase (6)<br />
• As you have seen, differences in the<br />
relative starting point of the three waves<br />
results in very different shapes to the<br />
resulting complex waves.<br />
• These differences in starting point are<br />
known as phase differences and these<br />
differences can be expressed as a phase<br />
angle (in degrees).<br />
Adding <strong>Waveforms</strong> & Phase (8)<br />
When we add together two waves that differ<br />
slightly in frequency (less than 20Hz), the<br />
resultant waveform has a very low F0 which can<br />
be heard as an intensity fluctuation, which is know<br />
as beating.<br />
Speech <strong>Waveforms</strong> (1)<br />
• A waveform is a two dimensional representation of<br />
a sound. The two dimensions in a waveform<br />
display are time and intensity. The vertical<br />
dimension is intensity and the horizontal<br />
dimension is time.<br />
• <strong>Waveforms</strong> are known as time domain<br />
representations of sound as they display changes<br />
in intensity over time.<br />
• The intensity dimension actually displays sound<br />
pressure. Sound pressure is a measure of the tiny<br />
variations in air pressure that we are able to<br />
perceive as sound. Intensity in these waveforms is<br />
a simple linear scaling of sound pressure (not dB).<br />
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21<br />
23<br />
Adding <strong>Waveforms</strong> & Phase (7)<br />
Here we can see 2<br />
waves (dotted lines)<br />
added together with<br />
different phase angles.<br />
At 0° and 360° (the two<br />
dotted lines are in the<br />
same place) we get full<br />
reinforcement.<br />
At 180° we get complete<br />
phase cancellation.<br />
In between we have<br />
different degrees of<br />
reinforcement or<br />
cancellation.<br />
Adding <strong>Waveforms</strong> & Phase (9)<br />
• If you examine the topic web page at:http://www.ling.mq.edu.au/speech/acoustics/waveforms/adding_waveforms.html<br />
you can see some examples of how<br />
adding different waves with different phase<br />
angles (or phase relationships) can result<br />
in some very different wave shapes.<br />
Speech <strong>Waveforms</strong> (2)<br />
• On the following pages, all of the diagrams<br />
represent the waveforms of the speech of a<br />
single male speaker of Australian English.<br />
• Time Scales: For figures 5 to 13 the horizontal<br />
time scale is indicated by the vertical dashed<br />
lines which are 100 milliseconds (ms) or 1/10<br />
second apart and the waveforms on these<br />
diagrams represent 800 ms (0.8 secs) of<br />
speech. For figures 1 to 4 the waveforms are 40<br />
ms (0.04 secs) long and there are no vertical<br />
time scale markers.<br />
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22<br />
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