The world of guitar and bass effects is a big one, with hundreds of unique stompboxes and effects units to choose from. Just about every player is familiar with the most common types, such as overdrive and distortion pedals, but there are tons of other effects to fill in all the little niches you may need to explore to create the sound you want. Harmonizer and octave effects pedals are the perfect examples of this: they're part of the pitch-shifting effects family, with the potential to dramatically transform your tone. These are the kinds of pedals to break out if you want to do things that would be impossible for a more common effects unit, when you really want to push the envelope.
For an example of what these pedals can do, let's start with a look at the straight-up pitch-shifting units. These are the sort of pedal that allowed Dimebag Darrell to pull off the insane 2-octave bends like in the solo work in "Becoming" - specifically, he used a DigiTech Whammy pedal, a few flavors of which you'll find in this section. Octave pedals are the most common type of pitch shift, and if you want to go all-out, they make it easy with options like the Electro-Harmonix POG2 Polyphonic Octave Generator Guitar Effects Pedal, which gives you control over multiple octaves at a time for a range of possible sounds that's just plain ridiculous.
If standard octave pedals aren't quite your cup of tea, maybe harmonizers are more up your alley. The Boss PS-6 Harmonist Pitch Shifter Guitar Effects Pedal is the quintessential example here, packing a boatload of versatility into its deceptively straightforward package. These stompboxes support blending in any common interval, creating a duet-like effect from a single guitar. You can think of them like chorus pedals with the added benefit of pitch-shifting to create an even more dynamic result - just the thing if you want a deeper, richer sound for that big solo. With a harmonizer's diatonic pitch-shift scales, there are all kinds of different harmonies available at the touch of a button.
Like any other pedal, every stompbox in the harmonizer and octave effects pedals family has its own individual personality and capabilities. So if you're not sure where to begin picking out the best one for you, try starting with the top sellers and see what the reviewers have to say about them. Nobody is more qualified to tell you what to expect from a pedal than someone who's played it, after all! Follow your instincts and factor in those peer recommendations, and you'll find the right harmonizer or octave pedal in no time.