Does the natural sign still apply with the octave up sign?

It's still a natural. True, the notes at that part of the bar are played an octave higher, but because it's written on that top space, and a previous E was naturalised (?) in the same place, it retains its accidental. A cautionary natural sign wouldn't go amiss, though.

1. Does a natural apply to all octaves?
2. Does key signature apply to all octaves?
3. Do accidentals apply to all octaves?
4. Does a natural apply to the whole bar?

Does a natural apply to all octaves?

9 Answers. Wikipedia has it right. An accidental that is written in, as shown in the example above, only applies to the note in that octave until the end of the measure. You may be confusing it with the accidentals in the key signature which do apply to every octave.

Does key signature apply to all octaves?

An accidental only applies to the note it specifies, at that octave, for that bar or measure. A change to a note in a key signature applies to every occurence of that note on the stave, at any octave, until the end of the piece, or the key signature is changed.

Do accidentals apply to all octaves?

Accidentals apply within the measure and octave in which they appear, unless canceled by another accidental sign, or tied into a following measure. If a note has an accidental and the note is repeated in a different octave within the same measure, the accidental does not apply to the same note of the different octave.

Does a natural apply to the whole bar?

Yes and yes. It lasts for the whole measure. Note: Most good editions will give a cautionary accidental in case there's a C on a different line to space than the one with the original natural sign on it.