What is a guitar synthesizer pedal?
The guitar synthesizer is a unit that emulates your signal into a tone that reminds of synthesizer, it kind of gives you the oppurtunity to play synth on your guitar. The first real model of this unit was the Roland GR-500, a pedal from 1977 that needed a special pickup installed on the guitar. So did many guitar synthesizers for a long time but today the technique has evolved so that this isn't necessary. Instead, modern units use pitch tracking and sends the information to an oscilliator, which is both simpler and gives the player better sonic possibilities. And gets rid of that extra pickup.
Any good examples?
Adrian Belew is an early user of the guitar synthesizer pedal which can be heard on King Crimson songs like "Discipline" and "The Sheltering Sky". Different artists as David Bowie ("Ashes To Ashes", played by Chuck Hammer) and Judas Priest ("Turbo Lover") has used the device and even guitar hero Jimmy Page has had a stint with this effect on "Who's To Blame". Andy Sumners used it on classic track "Don't Stand So Close To Me" by The Police and jazz virtuoso Pat Metheny employed it on his album "Offramp", which can be heard on songs like "Are You Going With Me?". A more modern example is The Mars Volta, where Omar Rodriguez-Lopez has used guitar synthesizer pedals on tracks like "Cicatriz E.S.P.".
Which pedal should I get?
These are pricey units, so make sure you try them out before you make up your mind. Many of those classic sounds comes from Roland units like GR-300, GR-500 and GR-700. A more modern take is the GR-55 or the GR-20, and these pedals have many of the same features as rela synthesizers: flute, saxophone, trumpet and so on. But even these more recent units needs that special pickup installed on your guitar to work. If you rather just plug and play without any hassle the Pigtronix Mothership or the Snazzy FX Mini-Ark might be what you're looking for. Or there's the pedals from Electro-Harmonix - the POG and the HOG - both used by Omar Rodriquez-Lopez and both really cool and well-sounding pedals. If you're interested in the world of guitar synthesizer pedals then check them out!