If I was to rate the three mentioned, I probably would select Korg, Ketron, and Yamaha in that order..
There is another I would select above all three...and that would be Roland, not because it is head and shoulders better than the others (it is not)....but the design is...the auto track, and auto detect are great..and chord analizing are great...Set up is a breeze compared to Korg, and results are superior to me..
The Korg OS is the downfall in setting up a harmonizer on the Korg...the effects blocks and routings are terrible..selecting harmony for a song (SMF) and than harmony with a style, or maybe real time voicing of harmony, is a chore on the Korg...Roland is way better in this behalf...

I don't believe the stand a lones are worth the hassle...on board is a better flow to doing things..
Roland lacks the gimmick things "scoop" and "d-essing"....(fake at best)..but the ability to make the harmony more usable in a live performance, is unmatched..

I have found that even long time Roland users, do not understand the Roland harmonizer on the G70/E80....They pass over "vocoder" mode thinking it is the 25 year old Korg vocoder..it is NOT!!
Select "My voice" and you can use this real time voicing harmony, and you can edit the zones, range and other parameters to suit your use..

Some of my experiences with the three mentioned...I already explained my disappointment in the Korg (OS)..I used a PA800 for awhile, and disliked the harmonizer....
My Ketron experience was the X1..Used it for about a year..the $116 harmony board (dealer cost) was worth having, but had glitches, and different harmony settings were a pain to keep set up..

My last Yamaha that I actually tried to use (harmony), was the PSR 2100...It was a nightmare...the final day, I was playing a Dept store, and comments from elderly shoppers, about the "funny" sounding vocal (not me)....embarrassed me...not only did I never use the harmonizer again...I got rid of the PSR 2100...and It's backup brother..

I also used a Tune 1000 Harmony box with my G1000(still have the Harmony Box)...It is a no frills harmony unit that actually did sound great...in fact in blind test, I had musician friends pick the Harmony Box over Digitech....I used the midi sets on the G1000 to make the Harmony Box more useable..

I think we can use any of the harmonizers ....but the important factor...don't over use them..pick your spots....

BTW: you can actually use a vocal sound (choir) etc, and create a touch of added harmony in place of no harmony options...

Maybe I am missing something, but I use the VH on my KORG Pa900 and I don't find it difficult at all ... I only use a couple of SMFs, but I've set up specific styles for songs, including the harmony voices I want, without a problem (I have created a number of different harmony 'presets') ... I can also change the harmony parts "on the fly' while I am playing a style ...
I don't think we can REALLY hear how the harmony sounds while we are singing, but I have had many compliments on it, especially from my most sincere critic, my wife ...
The only other VH I have used is the Digitech VH Workstaion ex, which also sounds great ...
Just my 2pennies worth ...

Tony I wish Digitech or tchelicon would make a new harmonizer with the same layout like Vocalist Workstation EX.Easiest thing ever to use.Very fast to set harmony when you play live.I wouldn't mind getting even original workstation EX in a good shape.

The vocal harmonizer on PA3x and PA900 are much easier to use than the one on the PA800, and to my ears is much improved. Actually the PA900 is more user-friendly than the PA3X, but lacks a few of the bells and whistles maybe.
Ketron is also vastly improved. The Midjay had only a vocoder. Audya is way better than the old X1. Roland is a non-player for now, so is not relevant. If the BK9 had a decent vocal harmonizer I probably would have kept it.

mirza ... I totally agree ... and the presets that are written to be used without a midi connection and follow your voice while only indicating the key you are singing in work great ...

Here it is:
http://www.ebay.com/itm/DigiTech-Vocalist-Workstation-EX-Vocal-Harmony-Processor-/191394944113
There are some power supply cords available on e-bay also ...

I had a problem with mine a while back and was able to find a pretty beat up one on-line that I bought for parts ... I sent it to the repair shop with mine and the techs were able to get mine working beautifully ...

These LOOK like they might work in the same way:
http://www.ebay.com/itm/Digitech-DOD-Voc...n-/111495661510

http://www.ebay.com/itm/DigiTech-Vocalis...l-/251686609392

I used Robbies settings on my S950.......EXCEPT I changed his Chordal selection 3Abv.Jazz.....to 3Abv.Chordal....
and Vocal Effect Type 80sPOP Rev to R&R Delay..w/ 16 rev.
This made a BIG difference in chord/vocal tracking my voice.

If you have a Yamaha S950 or T4/5 try these settings, just follow the video and stop it,.... make changes on your KB & continue, adding my edits along the way also. ....
it makes a big difference in the VH2 sound & tracking...

My 2 cents ..............

I started with a Digitech Vocalist 4 floor pedal model and have tried several different things mostly through rentals. Haven't found anything better. I wanted a PSR S950 but VH2 is so bad I bought the 750 instead and run my Vocalist through it.

Sometimes I think I hear decent harmony with VH2 but the whole processed sound is very unnatural. Even the lead voice becomes garbled when harmony is engaged.

This is what my Digitech V4 sounds like.......



All my You Tube postings use Digitech harmony.

God Bless,
Don

Having tried them all since the first Digitech came out, none, both onboard and outboard, really excite me. Additionally, the best use of any of them can be described in a single word - sparingly!

The S-950's onboard harmonizer, when properly tuned, actually sounds pretty good - not fantastic. However, when used sparingly, and when properly tuned, which DNJ has done, it can add a bit of body to a good vocal performance.

None of them sound fantastic, though. And, they will not change a bad singer into a good singer, or even a mediocre singer. That just ain't gonna happen. Some of the KJs in this part of the world utilize everything they can to improve the vocal quality of their followers. I've only heard one PC program that will do this, and I don't believe it's commercially available at this time.

Cheers,

Gary

I have no experience with the TC stuff. I have used Yamaha, Ketron and Roland. The G70 beats them all hands down. I played in Church a couple of weeks ago and after the service the choir director came running up and asked me how I recorded the harmony and got it to play back at just the correct time. She is a college trained public school choir director and was fooled by the G70.

I haven't had tons of experiences with different keyboard harmonizers.

That said, I have used Digitech and TC Helicon harmonizers with guitar...prefer TC Helicon.

My wife and I found that we needed different settings for her when she used both the S950 and Tyros 4 harmonizers...different than mine I should say.

Here, my wife is using the TC harmonizer system of the Tyros 4...starts at about 42 seconds into the clip.

https://www.youtube.com/watch?v=ubf-OJE_Xd4

The mike on the camera was so so in the clip.

Harmonizers do take a bit of tweaking regardless...at least the ones I've used.

Also, no harmonizer sounds as good, to my ears, as real vocal harmonies.