A chorus pedal plays a slightly out-of-tune copy of your guitar along with it, so it sounds like more than one guitar.
While the delay gets longer, the copy plays slightly lower in pitch. While the delay gets shorter, the copy plays slightly higher.
When the two sound waves match, the sound gets louder. When they are opposite, they cancel and the sound gets quieter.
The copy's pitch keeps changing, so the volume keeps going up and down.
A guitar note contains many frequencies. Each one gets louder and quieter at a different time. Together, that is the chorus sound.
The pedal keeps changing how late the copy is. Drawn over time, that is a wave. Delay is the middle of the wave, Depth is how tall it is, and Rate is how many waves a second.
Sets the middle of the wave: how late the copy is on average. Much shorter or longer delays make different effects.
Click a range to try it.
Sets how tall the wave is: how far the delay moves above and below the middle. More depth puts the copy more out of tune.
The range the delay moves through, and how far out of tune that puts the copy.
Sets how many waves a second: how fast the delay moves back and forth.
The delay moving back and forth over the last 4 seconds.
Sets how loud the copy is. When the copy is as loud as your guitar, the cancelling is strongest.
Grey bar: your guitar. Blue bar: the copy. The curve: how much louder and quieter the sound can get.
Each button sets the knobs and starts playing. Then change one knob and listen to the difference.