• Background
• Instructions
• Illustration
• Quiz

## Background

If you recall, when examining what light is, we talked about light as a wave. In examining waves, there are two important measures, their amplitude and their wavelength. Amplitude, for light, means the intensity or brightness of the light, and wavelength dictates the color. Sound has similar attributesâ€”amplitude and frequency (the inverse of wavelength). Both of these physical attributes maps onto a perceptual attribute. Amplitude maps onto loudness, frequency maps onto pitch. Here we consider pure tones, that is, sound waves in which air pressure changes follow the basic sine wave format. A pure tone is heard at a particular pitch but does not have the complexity you would expect when hearing a musical instrument (or a voice) play (or sing) that particular pitch.

In this illustration, you can manipulate the frequency and the amplitude of a sound to see how it changes our perception of a sound.

## Instructions

### Full Screen Mode

To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page.

### Settings

Below is a list of the ways that you can alter the illustration. The settings include the following:

Play: start the sound. The button will then change to Pause and pressing it again will stop the sound. Amplitude or Intensity: change the height of the wave; as the wave gets taller, the wave taller and the sound more intense.
Frequency: with sound we usually condider frequency, or how often the waves happen. Notice that they x axis is now time. The higher the frequency, the more waves will be in the graph. A 12.5 msec period of time is displayed.
Show Intensity: If checked, draw a vertical line from the 0 value to the first peak. The height of this line is the intensity or amplitude of that wave.
Show Frequency: If checked, draw a line connecting the first two peaks of the wave. The longer the line, the lower the frequency.

### Reset

Pressing this button restores the settings to their default values.