I searched the web for this question. I found some scholars answering that it depends on how Auto-tunes is used: if you are completely changing the voice to sound like music, it's haram, but if it's used just to improve the voice quality, it's acceptable. But I'm finding it hard to find a definitive Islamic judgment on this subject. Is there a fatwa?
I think this question is something like: Is knife Haram?
Having most of objects themselves is not Haram. Our usage of them can be Halal or Haram. If we want knife to eat fruits or kitchen work it's Halal, if we desire to injure some innocent it's Haram.
Auto-tuner can be used to play Quran, Halal music or Haram music. Having it is not Haram, but the application can be Halal or Haram.
And I said most of the objects, because some objects are made only for Haram use, like alcohol drinks or addictive drugs. Some scholars say having, selling or buying these types of objects is Haram also.
I'm not a scholar, but I will answer this question from the perspective of the general understandings of:
First of all, what is Auto-Tune (sometimes spelled as Auto-Tune**r**), from http://en.wikipedia.org/wiki/Auto-Tune:
So Auto-Tune is not a radio- or iPod-like device used to play audio as-is (be in Qoran, pop music or audio books). Auto-Tuner is a device used to alter the voice of the singer so that it sounds better (smoother, sweater) to the ear, in other words makes the voice not genuine.
Now, going back to the question, it is assumed that:
Different people have different physical and mental qualities. Each man excels in different areas. Where am I leading with this?
A person who is not an engineer shouldn't probably build a Masjid. What he can do is pay an engineer to build it on his behalf, but he should not claim that he built it with his hands. Doing so would be deceiving people. Not the best example, but I hope I made the point across.
Similarly, when it comes to reciting Qoran, a person with not-so-strong vocals shouldn't use Auto-Tune to improve (or fake) his voice as if he is using his natural voice qualities in recitation. Doing so would be deceiving listeners into thinking that the reciter has impressive vocal qualities which are worth admiration.
Instead, such a person should either use their voice as-is (as Allah SWT gifted it to them), or, if they are concerned about their vocal skills in front of a large audience or for the purposes of a recording, let someone else with stronger vocal qualities do the recitation. Using Auto-Tune to become a "celebrity" Quran reciter by "improving" their voice quality as if it was given to them by Allah SWT would be deception.
After all (since there's only one Quran with one content), don't listeners enjoy/prefer certain Quran reciters more than others particularly due to their vocal abilities?
To respond in a more pointed manner to the question:
"just to improve the voice" = "alter the voice". Which could also be equated to "fake the voice", depending on the following facet of the question:
After the voice is altered, is it disclosed that it is not the natural voice, instead Auto-Tune was applied? If not, then it's probably "fake the voice quality", which probably results in Haram.