starrynight

Most music is in a key, if it deviates from that alot people may infer it is out of tune. Also most people aren't used to microtones and they aren't generally used in music. So it's about conventions and expectations and they tend to be quite rigid for most people.

MoonlitSunshine

^ It's worth noting that the average human, even many with perfect pitch, can't hear differences in microtones. Most people who sing in choirs for extended periods of time can hear when the tune has gone more than a semitone away from the original key (though sometimes when it makes it the whole way to a tone it can be hard to tell that a change has happened), and a few people in experienced choirs (in my experience) can tell when it's dropped/risen noticeably, but less than a semi-tone.

As for the concept of "out of tune" there are two ways of looking at it.

1) The actual tune: A "tune" is a series of notes/tones in a particular order. Like Kaimon said, each note is succeeded by another note, which is a set amount above or below the previous note. Arguably, what notes you sing in order to sing this "tune" depends on what note you start on: so long as the relationship between each note, relative to the starting note, is the same as in the original, you are singing the same tune, just in a different "key".

Most people that I know can hold a tune that they know well, given a starting note. If they're always given the same note, they'll always sing in the same key, but if they are given a different starting note (without knowing, however: there are often some rather interesting side effects of asking someone who knows they are singing in a different key to sing a tune they just sang in another!), they will sing the tune properly, but this time relative to the different starting note.

As a result, you can sing "in tune" while singing completely different notes to the original piece, so long as the relative distance between each note is preserved. So say your original tune was AABBGGA, if you started on say, D, the "tune" would be DDEECCD. Singing "Out of tune" would be if you didn't do this: singing, say, different notes for some parts but not all (like AACCGGA), which then changes the relative distances between the notes. That would be singing "out of tune"

Unfortunately, as this post drags on, this isn't actually what's happening normally when someone is singing out of tune. Basically, for any note (I don't really want to get into the physics of this) there is a range close around it that can be construed as that particular note. The sharper someone's ear for music, the smaller that range is. Most of the time, when we say someone is singing out of tune, it's when they are attempting to sing a specific note, but are not managing to sing close enough to that note for those listening to think that they are close enough to the note (Obviously this is a largely subconscious activity - we in general don't go around constantly checking if someone is singing in key, but will almost always notice if someone is singing "flat" (too far below the note) or "sharp" (too far above the note) relative to our own ability to discern such ranges.

This is probably why people who sing out of tune don't realise they are singing out of tune: to their own ears, they are close enough to the note for them not to be able to tell they are "out of tune". To anyone with greater musical ability, however, the same cannot be said.

2) Relative tuning: This form of "out of tune" is related to the second part of the above, namely when someone is singing with other people, or accompaniment, or both, but are not singing the same notes. This, I think, is another case of the person not realising that they aren't singing the same notes. In this case, the "tune" can be perfect, relative to another key, but will still sound awful in tandem with everyone else singing in the "right" key (there are exceptions to this, but I don't think this is the time to be getting into the explanation of harmonies...). Generally though, in this circumstance if someone is singing that far off everyone else, the chances are they don't be singing the right notes even with respect to whatever key they've chosen themselves, unless they literally cannot hear those they are singing with.


I'm not sure if any of that made any sense, I kinda started rambling half way through it, but I hope it helps!

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starrynight

This is the crux of it, what the actual intention is.

On this I meant if a piece is full of microtones, in which case it is likely to be more noticeable. I don't know if there is a vocal style anywhere like that in the world, though there might be I suppose.

As I understand it all notes are likely to have some dissonant parts when expressed and are not completely pure when they are sung but we can't hear that.