To Do and Notice
The object of Tone Memory is to exactly match the sound of
the Static Tone with the variable tone from the Tone Slider. There are three ways to do it: from memory, listening to the "beats", (read "What's Going On" for a definition) or cheating!
Matching by Memory
- Select the Static Tone button and press Play. Remember what you hear.
- Click anywhere along the Tone Slider to move the slider to a new tone.
- Select the Variable Tone button and press Play.
- Do they match? If not, go back to step 2. If you think they match, click the Show Frequency button.
Matching by Hearing the Beats
- Select the Both Tones button and press Play.
- If you hear two tones at the same time the tones are not very close. If you hear "beats" the tones are pretty close. If you only hear one tone you've found the match!
- If you haven't matched the tones, move the Tone Slider, press Play and try again!
Cheating!
- Select the Show Frequency button to compare the numeric frequencies of the two tones.
- To hear some cool beats, set the Tone Slider to 439 or 441 and press Play (with Both Tones on).
What's Going On?
With Tone Memory, you can test your ability to remember tones and you can hear interference or "beats" between sound waves. Sound waves can meet and cancel out; that's destructive interference. They can also meet and amplify each other; that's constructive interference. It depends how the waves meet. When they meet crest to crest, it's constructive. When they meet crest to trough, it's destructive.
If two tones are close enough in frequency, their wave forms interfere constructively and destructively, resulting in an audible rhythmic variation in loudness. This is called "beating".
You also can listen to the Tone Memory Exhibit
(658 Kb) just as it would sound if you were at the Exploratorium.
So What?
Beats are used to tune pianos or guitars. The closer the tones are to each other, the slower the beats beat! Moire patterns are the visual equivalent of beats.