Sound Is a List of Numbers

Lesson 5 of 11 · 7 min · Free, no account needed

What you will learn

A microphone turns sound into a wave; a computer samples it: measures its height again and again.
Sample rate: how many measurements per second. A CD takes 44 100.
Bit depth: how many levels one measurement can have. 16 bits give 65 536.
Size = samples per second x bytes per sample x channels x seconds.

A microphone hears a wave of air. A phone can only store numbers.
One of these is the real sound, the other went through a cheap recorder. Play both. Which is the original?
Be the recorder: measure the wave.
Tap the wave in at least 8 places. Each stick turns its height into one number.
How many measurements make it sound real?
Turn up the samples per wave until the copy is at least 95% alike.
Samples, rate and depth.
A sample is one measurement of the wave's height: one number.
The sample rate is how many samples per second. A CD uses 44 100. Too few and the sound turns robotic.
The bit depth is how many levels one sample can choose from. A CD uses 16 bits: 65 536 levels.
A cheap recorder has only 3 bits: 8 levels.
Drag each stick top to the nearest level. The orange strip shows the error you are forced to add.
A CD takes 44 100 samples every second. How many in one minute?
Drag the marker on the scale. Each step of the scale is 10 times more.
Tune the whistle: match each target pitch.
A higher note is a wave that repeats more often. Lay your blue wave on the dashed one, then Lock in.
Play back your own numbers.
These are the measurements you took. A speaker turns them back into sound.
One minute of CD music: 44 100 samples a second, 2 bytes each, 2 ears. About how many MB?
1 MB = 1 000 000 bytes. Round to one decimal.
Back to the two sounds. Now you can see them.
Play them again and tap the robot.

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