Description of the sound waves

Sound waves exist as variations of pressure in a medium such as air. They are created by the vibration of an object, which causes the air surrounding it to vibrate. The vibrating air then causes the human eardrum to vibrate, which the brain interprets as sound. Sound waves travel through air in much the same way as water waves travel through water. In fact, since water waves are easy to see and understand, they are often used as an analogy to illustrate how sound waves behave.

Sound waves can also be shown in a standard x vs y graph, as shown here. 

This allows us to visualise and work with waves from a mathematical point of view. The resulting curves are known as the "waveform" (i.e. the form of the wave.)

In waveforms of speech, the x-axis represents time and is usually scaled in seconds or milliseconds, while the y-axis shows amplitude, a representation of loudness.

In the next image, it is shown three different sound waves, each with a different frequency. As you can see, the more cycles on the wave, the higher the frequency. All three waves seem to have pretty much the same amplitude, because the displacement from the zero line (not shown, but inferable) is very similar.

Finally, we can conclude this section with the different types of sound waves. 

• Not all waves are periodic
• A sound wave that does not have a regular pattern is termed aperiodic
• An aperiodic sound results from random, irregular vibration: noise
• Voiceless sounds have aperiodic waveforms
• Some speech sounds employ voicing and noise together: mixed waves

In the next post we will start studying the phonemes. :-)

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