I have used the TC Helicon VoiceLive pedal a lot live. But only for background vocals.
I have it setup in chord mode mostly. So it watches the guitar part. When I sing, it pitch corrects me to the closest pitch in the chord I am playing. From there the harmonies are relative to that note.
So for example, I can sing the 3rd and 5th above the lead by singing the 3rd and the TC harmonizes that.
The mic preamp in that thing is actually pretty good as are the EQ and compressor too.
You have to sing a strong part with good ins/outs to get the harmony to sound right. But it works well.
If you are using wedge monitors, you have to watch the levels too. If the harmony is too loud and your vocal mic is picking it up, it will get warbly when it re-harmonizes with itself.
Same for acoustic guitar. If the guitar is picked up by the microphone too loud, it will be processed by the pitch corrector and/or harmony generator.
But, the TC unit has very easy configuration for footswitches to turn the harmonies etc. on/off so you can do things like address the audience etc.
Richard
Pretty much same experiences here but with different products.... so, couple of sets of feedback here.
1. Got a good deal on an Antares AVP-1 on evilbay a number of years ago. Used it as an effects unit for lead singer in band. Pitch correction was fairly good but added artifacts to the output if not adjusted VERY carefully. Experiences pretty much matched those listed here..
http://www.antarestech.com/news/reviews/Antares_AVP-1.pdf
2. I initially bought the Harmony-G to "enhance" the backing vox I was doing for the band. I quickly learnt that adding a harmony to my [already] harmony line using a guitar [chord] input as guide, did not work well at all... in fact.. it was
TERRIBLE. It worked far better with some tweaking and
no guitar input, but that method produced inconsistent results. It worked fine as harmony (with guitar) for lead vox. No PITCH correction on that one but REALLY good harmonies.
3. I added a VoiceLive-2 last year.. to give the band (me) more vocal flexibility. Here, my experiences reflect those of Richard's above. The pitch correction is good, but one needs firm vocals for tracking. Harmony ranges/capability are absolutely unbeatable. The "tone" button - which basically makes your vox "FOH ready" - is great for solo use, but we found our soundguy preferred to have that control, and didn't want to give it up to a "black box".
In short, the pitch correction works fine... but it takes getting used to.
One BIG thing I learnt with these devices is (like vocal compression) do NOT put the vocal effects into your monitor mix. Where the device allows,
*send a separate harmony feed to FOH* where possible - IOW, do
NOT blend your vox with the harmonies/pitch correction/effects into a single feed. It will
*mess you up* and if - like Richard stated above - it gets back to the mic and attempts to harmonize the harmonies, it gets REALLY messy.
YMMV
Update: - I guess richard beat me to it on the separate feed to FOH part..