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    Well, key signature are a notational notion. – Édouard May 11 '14 at 16:06



But such scores are rather hard to come across.


Most scales are assumed to be octave-repeating, due to the way that we hear a similarity between notes that are an octave apart (the reason for this being that with many instruments, any note contains harmonic partials at the frequencies of all the overtones of a note an octave below).

This includes the diatonic scale, which is the scale that standard notation assumes (and that key signatures are most relevant to), and this is why key signatures are read as applying to all octaves. Hence why in your scenarios all 'A's will be flat unless otherwise indicated.

Incidentally, there do exist scales which are not octave repeating, e.g. http://en.wikipedia.org/wiki/Bohlen%E2%80%93Pierce_scale.

(adapted from duplicate question Are tonal (sharp, flat and natural) key signatures octave specific?)




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  • I don't believe that's the reason key signatures were invented -- they avoid unnecessary clutter for the reader. – slim Jun 27 '14 at 10:54

Truth is that it IS flat; however if you played A natural up high it wouldn't sound too bad because it's so far away in frequency terms. If it sounds "ok" then that's why.

  • Downvote? It's totally valid to play an augmented (sharp) fifth in a musical piece. I answered the question correctly. – Jason Locke Apr 1 '15 at 19:38
  • Of course - there's no 'invalid' in music - but whether it would sound OK depends on the context, not just the register. Indeed a low ♮A might sound great in some contexts. – topo Reinstate Monica Apr 2 '15 at 22:54
  • You implied that a high A natural wouldn't sound too bad. That was, I guess, if it was supposed to be an Ab instead. Then in the comment, it gets changed to +5, which is totally valid, but at that point, written as such, it is supposed to be played as +5, and will sound better than 'not too bad'. – Tim Feb 9 '17 at 16:03

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