How Sound Works

• How sound travels through the air
• How computers hear and play sounds
• Experiments you can try

DON'T USE HEADPHONES

DON'T USE HEADPHONES

PLEASE, DON'T USE HEADPHONES

Some demos can have very loud, annoying or even painful audio. Don't use headphones. Some demos may require the use of headphones: please check with a grown up first! Using headphones with loud audio is bad for your hearing health.

How sound travels

Notes

• Sound travels through air. You can feel air pushing or pulling things (like the wind!)
• It travels through air the same way waves travel in a pond when we throw a stone.
• It travels even if air doesn't "move": you can test this by doing a wave (like in a stadium). The wave travels through a group, but people don't move.
• When this wave of air "pushes and pulls" very quickly in our ear, a tiny tiny amount, and thousands of times a second, we hear sounds.
• Try it out: You can feel this as a vibration on your throat while you speak, or while you hum different notes
• Also: put your hand on a speaker, and hear (feel!) different sounds. Does the pitch make a difference on how the vibration feels?

How computers hear

Notes

• For people: sound is what our ears detect from air "wiggling" very fast.
• For a computer: sound is when a microphone or a speaker vibrates. When something vibrates, it wiggles a tiny bit, moving up and down.
• A computer's (or phone's) microphone will measure how much movement that vibration creates, and it will store a number.
• You can't measure this with a ruler! The movement is so tiny that you can't see it with your eyes.
• But we can cheat and "see" the measurements a computer stores by using a program.
• The animation below is a representation of a microphone. If the "wave" is taller, it stores bigger numbers. How do you think the height of the wave affects the sound? How does the number change if the wave starts closer to the mic?

How computers play sound

Notes

• A speaker does the opposite of a mic: it reads a number, and will move as far as the number says, very fast.
• A computer will "remember" a list of numbers that make up sound. This can be a list of numbers that makes music, or a list of numbers that records how you speak. It's all just numbers. A very very very long list of numbers: a computer will remember 48000 numbers for every second of audio it records!
• Because it is all numbers, a computer can change how things sound. For example, we can make things sound louder by multiplying every number in this list by 2. If you are a computer, it's important to know your times tables.
• The animation below is a representation of a speaker. How does a taller wave sound? What does the amplitude control?
• How will the wave sound if it wiggles more rapidly? What does the frequency control?

Frequency Amplitude Enable sound

Real sound: just numbers!

Notes

• We have been playing with very simple sounds, like the one in this demo (no headphones here!). Simple sounds help us understand how things work
• Real sounds are more fun, so let's use real sounds now. But before, let's review (you can use the example below to remember):
  • Sound travels as very fast "wiggles" or "waves" through the air.
  • How does sound change when waves are taller or shorter?
  • How does sound change when waves wiggle faster or slower?
  • How do computers record sound? And how do they play sound?
• Now that we remember how sound and computers work: let's record a few real sounds with a computer. Audacity is a good program to do this, freely available in any computer.
  • Record a simple sound (a test tone). Zoom in very very close: see how the shape resembles a wave (like in the animations here!)
  • Look at a sample: it's just a number! Can you count how many there are in one second?
  • Now record someone playing an instrument. Does it look simple, like before? Do you see how the waves wiggle faster or slower depending on pitch?
  • Now record someone talking. Can you see the changes in pitch, or is it so fast that now you can't?

Start No headphones here! Frequency Amplitude

The shape of sound

Notes

• We can recognize who is talking, and we can also recognize music and melodies. How do we do that? Each sound has a shape.
• We can't just look at samples. There are too many! There is a trick that lets us see the shape of sounds in a simpler way.
• Open the "spectrogram" (this is a fancy way of saying "drawing of how pitch changes with time"). Make just one sound (one phoneme: a sound like "AH") into the microphone.
• Your voice is made up of many different pitches, in a complex pattern that changes with time.
• See how vowels like "O" or "A" have a lot of low pitch, and consonants like "S" or "T" are mostly high pitch. Also try musical instruments, and clapping. Can you see the different notes?

Use this demo to test different sounds (no headphones here!) or open the frequency graph in a new page to see it better

Source Your mic Sine Triangle Sawtooth Square

Science experiment time!

What follows is a list of experiments you can try with sound and computers. Some require microphones, speakers, or both. Pick one depending on the equipment you have.

Speed of sound

• Sound is fast, but it still takes time to travel. Let's measure how fast!
• You need two microphones and a mixing console (this is a complicated setup!).
• Place them close together, start recording (with Audacity), and clap. You should see two waves starting at the same time.
• Now move the microphones far apart. Clap again, very close to one mic.
• Waves start at different times! You can use this to measure the speed of sound.

Notes

• Sound travels about 350 meters per second. It would take a full second to cross a football field, and 4 minutes to go from London to Brighton.
• That seems fast, but imagine waiting 8 minutes for someone to answer? And imagine how loud you'd have to shout!

Forget how to read

• You will need a mic and headphones (a phone works; make sure to use headphones. Careful with the volume!)
• Grab a book and click start. How much of a page can you read?

Notes

• You always hear yourself when you talk. This helps you control how loud you are. (Side experiment: block your ears and try reading a book. Ask someone else to tell you if you are shouting)
• Normally you hear yourself right away, with no delay.
• This demo adds a small delay (an echo). When you hear yourself with a delay, your brain gets confused and you forget how to read!

Start Delay Attenuation

Your hearing range NO HEADPHONES!

Notes

• We can hear very low and very high pitches. But everyone hears a little differently. How well you hear also depends on your age, and how well you've taken care of your ears.
• Your ear is full of little hairs that "dance" with sound. Like this one
• As you get older, or if you listen to very loud sounds very often, some of those hairs stop dancing. Make sure you take care of your hearing health!
• Play with this slider (NO HEADPHONES!) and see what's the highest pitch you can hear. Compare with an adult: who can hear higher?

Start Pitch Volume

Test tone generator

DON'T USE HEADPHONES HERE

This isn't really an experiment, just a way to generate simple test tones that can be used for other experiments

Start Frequency Amplitude