A synth pedal will provide you with a nostalgic range of tones, taking you all the way back to the heyday of the '80s! Emulating a classic synthesiser sound to make it possible for guitarists to attain a variety of electronic-style tones, synth pedals have become increasingly popular. With the renaissance of mainstream electronic music and acclaimed series' such as Stranger Things using synths exclusively in their soundtracks, there's a reason why these pedals are more in demand.
So, how does a synth pedal work? Most synth pedals work by detecting the pitch of your guitar's signal, and using that to tune and engage an oscillator. So whereas something like a modulation pedal modifies and processes your signal, the synth sound will actually be generated by a functioning synthesiser circuit within the pedal.
A good synth pedal will therefore give you loads of tonal flexibility similar to their full-fat counterparts, with a variety of controls that let you tweak the waveform shape, attack, decay and more. As a synth adds loads of extra harmonic content to notes, guitar synth pedals will often feature octave up/down functionality, and sometimes further intervals to give you the thickest and fullest sounds possible.