A guitar loop pedal allows you to lay down a short phrase of chords or riff that you can play over and over again. This can be a fantastic practice tool for improving your rhythm chops as well as your creativity and imagination. Loop pedals can also be used live to add an additional layer to a song and some musicians do this regularly, for example Ed Sheeran often uses a looper to create backing music for his jazz improvisation.
A loop pedal works by recording a signal from your guitar on to a tiny chip inside the standard foot pedal and then playing back that exact same signal at a time set by you. There are a variety of different sizes and shapes of loop pedals with a wide range of capabilities and capacities available. Some are designed to be a single pedal while others are multi-pedal devices that can record multiple overdubs.
The first step to using a loop pedal is to get familiar with the basics and practice using it. Then experiment with creating different layers. You can do this by adding other instruments such as vocals to your loop or try playing a scale against a chord sequence that you have recorded on the loop. Alternatively, you can use the pedal to play a whole chord progression and then add ornamentation such as strumming a muted string or scraping the side of a pick across the strings to create percussive effects.
You can also experiment with adding other effects such as a chorus effect or distortion to the loop. This will change the tone and feel of the loop and can help you to create a more unique and creative sound. The next thing to do is to try experimenting with the rhythm of your loop by trying to match it to a beat or groove that you are playing. Many loop pedals have built in metronomes to make this easier but you can do this by playing a muted string to set the tempo and then improvising to it.
Once you are comfortable with the basics of using a loop pedal try experimenting with creating different chord progressions or riffs and then add additional loops on top to create layers that build a composition. You can then use this composition as a backing track for practicing your rhythm skills or use it for improvised jamming with friends. Eventually you may even want to try to compose a full song using a loop pedal.