As redundant as this may sound, sequencers are devices that play sequences. This can be a melodic series of notes, raw voltages, rhythmic gate or trigger patterns, or some combination of all of the above. The length of a sequence is usually measured in steps, and a step will usually correspond to a musical length of time such as a sixteenth note. The sequencer will advance step by step through the sequence in time with the clock signal and reset once it completes all of the steps. As it passes through each step, it will output whatever parameter has been set for that step. For example, each step might have a note from the major scale, so as the sequencer strides through those steps it will play a melody.
Some sequencers are able to be reset through trigger inputs to ensure they start at the beginning of their pattern in tandem with other sequencers. In order for sequencers to remain synchronized once they begin playing together, they will need to share a common clock signal. In order to set this up, one sequencer will be assigned the “Master” and will run on its own internal clock. The Master then outputs its clock to any other sequencers that will then be set as “Slaves”.
Sequencers take many forms in the world of Eurorack as they are a very important part of making electronic music.