Autotune CAN NOT work with polyphonic signals. It can only work if one note at any given time is entered. It is impossible for it to detect 3rds...etc. As long as the recorded instruments are in tune, then all you have to do is use autotune on the vocal and it will be in tune as well. Figuring out the key is not really important at all in graphic mode unless the vocalist is so far off that he/she is singing notes closer to the wrong notes than the right ones, which is actually the case sometimes. Are you trying to use autotune to define a melody? Maybe I don't quite understand. Autotune is a tool usually used after a vocal has already been done. I have used it in this way, however:

Record a fairly decent (time is more important than pitch) vocal and autotune it. Then have the vocalist sing again with the autotuned vocal in the mix as a reference. Throw away the autotuned vocal or use it really low in the mix with tons of compression and eq. This will give the singer a really good idea of the notes to be sung, but won't make the take sound autotuned. Good luck!

Neil

However, he isn't confident in his ear hearing any out-of-tune notes, and wants to use Autotune in this method:

1. Place autotune onto the master fader, find out the overall pitch curve of the mix.

2. Compare the vocal's pitch line with that line.

3. Match the vocal's pitch to the song's overall pitch.

Nope. Doesn't work like that, and it isn't meant to. (I'll refrain from making any comment about how good a singer could possibly be if they can't hear out-of-tune notes... that statement alone should have set off warnings!)

'm finding quite quickly that using Autotune on a non-vocal track gives you what looks to be a bloodsplatter

AutoTune can handle "non-vocal" tracks just fine, as long as they are monophonic.

I am thus looking like an idiot to my client, a very bad thing.

Of course, reading the manual first might have prevented that. Don't get me wrong, I'm all for experimenting in the studio, but should at least have a small understanding of what your tools do and how to operate them before using one in front of a client.

Is it / how is it possible to find out if a vocal is out of tune without having a reference as to what the tune of the vocal should be?

What do you tune a vocal to?

You tune it to the same reference that you tuned your instruments to... probably A440. http://en.wikipedia.org/wiki/A440

How do I find out the key of the song if all I have is a few scratch tracks of the song and a 'finished' vocal?

That is generally more than enough musical information than you need to find out the key of the song (for most genres, anyways). Any real musician willl be able to do this for you, all you need is a grasp of basic music theory.

I'm sorry if I am coming across as condescending, I don't mean to at all, but some of your statements are very suspicious for someone who is getting paid to record people.

Apparently, "other studios" have been able to do as he requests. I realize that the manual states that monophonic sources are the only thing that autotune will recognise; how other studios have shown him what he's wanting to see on one graph is a mystery to me.

It's all just about a moot point now, however, as my ILok just went out yesterday in the middle of a session, once again making me look like an idiot.

:oops:

After the two (or more) weeks the ilok site states is needed, we'll see where I am at.

The manual includes a very good tutorial along with a sample to use. Takes less than 4hrs to go through the tutorial, experiment and get a grasp as to what is happening.
Afterwhich you would have come to the same conclusion as TommyJ above, that it can't be done in the 3 step procedure you outlined. (What does 'overall pitch curve of the mix' even mean?)
I'm guessing that if your singer is unknowledgeable about his own singing, he's probably even less knowledgeable about engineering techniques. Perhaps there are several steps missing in his recepie?