This is really exciting — as someone who spends far too much time messing around making electronic music, I was thinking about how cool it would be to have a voice-to-instrument converter. After all, if a computer can create the sounds of an orchestra or band with just your vocal beatboxing / humming chops and a sprinkle of machine learning, then that's all you need to make the next hit-song, right?

Well — not trying to detract too much from this field — but, that's where I think the expectations of grandeur, that some people will get about this emerging technology, are kinda wrong. There are a few issues I can think of that will need to be overcome (if even possible?) before this technology can be considered groundbreaking.

From the 'person' side:
(1) - Vocal range and ability >> This one is going to be most hard as most people can only sing within a couple of octaves, and even then, need quite a bit of 'tuning' help to identify the right notes / intentions.
(2) Musical theory >> Fitting into the above, if you don't have any musical theory knowledge (about what key you're supposed to be in, or about chords, or progression), then a machine learning process would have to fill-in all the chords and textures / build-up. But that really can only help you so much, unless you're just interested in the 'novelty' aspect of it.

From the 'machine' side:
(3) 'Bum' notes and 'quantisation' >> I noticed from the samples that the saxophone would produce flutter around a note, and also the timings weren't 'on the beat' — but this should be quite trivial.
(4) Expressiveness >> Right now, the instruments might be adjusting to the input velocities (loudness), but if you want a life-like sax sound then you'll need to produce a level of expressiveness that makes it sound realistic... This can be achieved with a mixture of better (available) virtual instrumentation, and also ML to figure out what the best intentions are of the input

I think the two big key factors are musical theory and expressiveness. With the former, I think anyone who has a good enough understanding of musical theory probably wouldn't have much of a use for this other than a novelty until it produces compelling, effortless results. This is because they're most likely to have some kind of instrumental knowledge (keyboard most specifically for virtual instruments) and music composition experience. The two groups this kind of tech would really help are a) very good vocalists who have no electronic composition experience but a good grasp of music theory — Michael Jackson is a good example of this as this is how he made his song ideas[0], and b) music producers / instrumentalists that want to 'fill-in' a lot of parts quickly by humming / beatboxing — but again, they can probably do this with a keyboard reasonably effortlessly. If the 'expression' is worked on a lot, then it will become more interesting as expressive effects are hard to get right without expensive hardware. [1]

As much as I appear to be 'bashing' this, I am reservedly excited — but can't help but feel if there actually will be a worthwhile market for the tech!

[0] - http://www.nme.com/blogs/nme-blogs/the-incredible-way-michae...
[1] - http://www.musiciansfriend.com/keyboards-midi/yamaha-wx5-mid...

EDIT: formatting