This is a pretty cool pedal from Electro-Harmonix that combines the features of a harmonizer and a vocoder into a pedal that can be hooked up to a vocal mic. The interesting feature that separates this box from other similar products is that it automatically adjusts the harmonies that it produces to an accompanying instrument. This is achieved by plugging in said instrument to the instrument input. There are inputs for both the microphone and the instrument, as well as outputs for each. The instrument output is dry (meaning there is no effect on it) while the microphone output is affected.
This pedal isn't the easiest one I've ever used, but once you get used to it it gets better. Mainly, having to hook up the second instrument was strange to me. However, once I got used to the idea, it became better and better. There are knobs for adjusting the sound as well. The first knob blends the dry signal with the wet one. The next two knobs are reverb; the first adds reverb to the dry vocal, the second adds it to the effect vocal. The "gender bender" knob adjusts the timbre of the vocal to make it sound more "feminine" or "masculine", but those terms are rather limiting. The effect comes out rather androgynous no matter what setting you use. The voice mix adjusts the frequencies highlighted from low to high. The mode knob simply changes the mode that you have selected. There are several modes; one for low harmony, one for high harmony, one that switches, three multi-harmony settings, an octaves setting, a unison/whistle setting, and the vocoder setting.
The sounds that come out of this box are certainly interesting to say the least. While they could be considered to be pretty artificial sounding, I don't think anyone really expects the pedal to sound like multiple singers. That being said, it's a pretty interesting thing to use when performing solo. If you want to get an idea of how to write harmonies for a certain chord progression, this can be a great tool. It's also really fun. It can make playing solo far more lively and entertaining. The vocoder sounds are arguably the most useful, considering the quality of the sound. That sounds almost like a traditional vocoder with the full keyboard. Some of the harmonies aren't as useful, and there are tuning issues when using it with a guitar, but I think most people would be happy with this pedal.
I think that this pedal is a great tool for exploring harmonies to an extent, and the vocoder setting is really cool. However, I didn't really get much use out of this other than the obligatory messing around. I wouldn't really use this much in a live setting or even recording, except maybe for the vocoder. I'd say that if you have a profound interesting in artificial harmonizers, than this is probably the cream of the crop. Otherwise, it's probably best to avoid it.