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A waveform is the shape of a wave. To the right is a graph of a waveform for a sound wave created by a clarinet. Sound waves are created by changes in pressure

waveform for sound waves
Sound waves created by a clarinet. [Image source: Rburtonresearch – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=45035734]

of a medium such as air. The horizontal axis shows the passage of time in tiny fractions of a second. The vertical axis shows air pressure. Atmospheric air pressure which would prevail if there were no sound at all is indicated by 0, in the middle of the vertical axis. Different pitches are created as the air pressure increases and decreases.

waveforms with different frequencies and wavelengths
Waveforms shown schematically. [Image source: modification of own work, LucasVB, https://commons.wikimedia.org/w/index.php?curid=1536518m, Retrieved Feb. 10, 2018.]

The diagram to the left shows waveforms, schematically, that represent the increases and decreases in pressure of various sound waves. As in the image above, the horizontal axis is time and the vertical axis is air pressure. The waveforms higher on the chart represent higher frequency, that is, higher-pitched sounds. The waveforms lower on the chart represent lower frequency, lower-pitched sounds.



waveforms schematic
[Image source: By Omegatron – Own work, https://commons.wikimedia.org/w/index.php?curid=343520. Retrieved from https://en.wikipedia.org/wiki/Wave Retrieved Sept. 21, 2017]

Some waveforms flow smoothly and others, when graphed, take more angular or jagged forms, as in the accompanying diagram to the right. Again, time runs across the horizontal axis and some phenomenon, let’s say the intensity of a light, runs vertically. Consider the square waveform, the green line, for example. It shows that the light intensity remains at a high level for a bit of time, drops to a low level for the same amount of time, returns to its high level for the same amount of time, drops…etc.