Is there an unwritten "rule of thumb" in notation for deciding whether or not to change the key signature, if you are temporarily in a different key and intend to return to the first key? Like, "5+ measures in a new key, change signature"?

No.

That means you can make one up if you want to.

P.S. Maybe there is some guideline that I'm not aware of.....let the composers sing out if there is.

I think what most do is write in the sharps or flats without notating a key change.

But sometimes not. Sometimes the key signature is changed for a stretch.

The question is whether there's a guideline on when to do that or not.

hmmmm, maybe I should have also added: does it matter what level the music is written for? For those more on the beginner side, is it harder to wrap one's mind around a new key signature suddenly appearing, or a slew of sharps and flats and naturals for a few measures? Thanks for the input so far!!!!!

It's a matter of judgment all the time, and the things you just mentioned should factor into the judgment.

Thanks for pointing me in the right direction.

Can't tell if that's 1% or 100% sarcastic.

Anyway......your prior post didn't address the question, did it?

3% sarcasm. 97% good intentions.

fair enough

IMHO 5 bars is not long enough to warrant a change of key signature. I'd change the key signature if an entire section went sharpside. A good example from my student days was a Brahms piece for organ, the fugue in Ab minor. The middle section is in D major and the key signature changes appropriately (because Ebb would be too much trouble). Which brings me to another point, if the key change is just 1 or 2 sharps or flats it's probably not worth the trouble. That's my $.02.

Another related question is how to notate a passage that has clearly left its "home" key and stays "up in the air" for an extended period of time. I can't remember which piece this was, but I played it in a chamber group at school. A passage in the development section started climbing up the circle of fifth so fast, something like the whole circle within 30 bars.

Two issues cropped up -- the first was that what "key" could that passage be assigned to? The answer would really be "none", and would it then make sense to keep the original key signature, or would it make more sense to go into a "neutral" key?

Another issue is what to do when the passage gets "so sharp" that it becomes impractical to notate in such a way as to strictly preserve its harmonic meaning? At some point, a I-V progression must become a I-vi(dim) and sharps must become flats. However, I remember that on that particular score, a certain bar was clearly in "A# major", modulating into the "E# major" by the next bar. The notes weren't spelt as Bb going into F, but literally as A# going into E#, with all the glory (and pain) of double sharps :S Now, while that was gallantly grammatical, I found it a pain!

Thanks again everyone for your input. Tar, I will have to read your post at least 4 more times before I understand it! ha Actually I do understand what you were getting at, (somewhat), but from my point of view, doing the double-sharp thing in the name of "proper" rule-following is completely ridiculous! I suppose to the truly theory-minded it is somehow helpful, but I would guess to the more lower-level player, it just puts the music into the realm of unreadable obscurity. On the other hand, my notation is probably often improper, as I tend to notate based on how a passage "feels" to me or how my mind seems to interpret it. Which can lead to, say, a flat key suddenly becoming a sharp key at modulation. Technically speaking it probably is just another flat key, but somehow it doesn't "feel" like it to me. Or, perhaps in a given case, I opt to change from flats to sharps and thereby have one or two less accidentals in my key signature, which I would hope would be less intimidating to a beginning player. Incidentally I think it's kinda sad that the notation for keys with lots of black keys looks so cumbersome, since I think it is so much easier to play things with lots of black notes...seems like those sorts of keys "fit" your hand more easily and allow for much more fun in terms of having hands work underneath or on top of each other. But I think beginners...or heck, I guess even I feel this way at times....look at a key sig. with 5 or 6 accidentals and start getting just a tad nervous....

Incidentally I was reading some music that switched twice between...maybe 4 flats and 5 sharps, or vice versa, or maybe it was 5 and 6; anyway, I was commenting to my husband (who doesn't play piano for fun although he can figure stuff out) that it was very confusing because every time there was a natural written in (which was often), it had the potential to trip me up as I had to process whether or not I was moving "up" or "down" from the notated pitch (based on key signature). (Esp. when there were naturals or extra accidentals written in both hands.) He did not understand this at all, and said, "but an a-natural is an a-natural!" True. Which made me realize something that perhaps had been more unconscious: that maybe once I get going, I'm not really thinking in terms of key signature any more. And 5 flats is fine, you just get yourself oriented and go with that, but the switches from many flats to many sharps was messing me up in that orientation. I just thought that was kinda interesting.

See, this is where -- if I had my own way -- I'd strip the passage of any key signature and write out all accidentals explicitly. It's always an issue when one is in the "transition" between a very sharp key and a very flat key.

Yet, if a piece was already in 5 sharps and I wanted to switch to 4 flats (which could be rewritten with 8 sharps), I personally wouldn't mind a couple of double sharps so much. Similarly, if the piece was already in 5 flats going to 6 sharps (= 6 flats), that's only 1 flat difference and I think it would be both grammatically nonsensical and visually ridiculous to switch key signature in that way. Going from Db major to F# major is an augmented third shift, which is a very, very awkward way of saying a perfect fourth.

That said, I guess one just has to be sensible and not going so far as trying to call Bb major with 2 flats as "A# major" with 10 sharps!

And I agree, it is a shame that many black-note passages are actually easier to play even though they are scary looking. I wonder how off-putting it would be if a child were taught "Chopsticks" by sheet music with 6 sharps (or 6 flats) rather than by watching another child doing it!

I certainly prefer this if I'm reading music which is highly chromatic with shifting tonal centres. And in fact if there's no strong tonal centre there seems little point in having a key sig.

In writing it can be clearer to change the key signatures (that is, you're less likely to make errors), but I found through experience with one of my pieces that string players in particular would prefer the accidentals to frequent key signature changes, though they were pro players and took everything in their stride.

Yup,

I haven't used any key signature for a long time... And for a few pieces I also don't use time signatures... heh...

What about instances, i think i have seen this a few pieces notated with non-standard key sigs (Bartok's Mikrocosmos??), may be because the piece doesnt follow the standard Major, Minor scales. What about if its based on modes, the key signature at the beginning indicates combination of sharps and flats on those notes unlike standard key signatures. Also the question would be can we use Finale, Sibelius to notate non-standard key signatures?

Yes Bartok does that a bit in Mikrokosmos. I know Finale can do that, I'd be surprised if Sibelius can't.

As for whether or not to use a key signature at all, I think it depends on whether or not the piece follows a tonal center and follows tonal "rules". If so, then a key signature would probably be beneficial, as writing in a key signature brings with it the implication of a key center and certain rules/patterns. However, if a tonal center or tonal rules are not largely present, then yeah, that could be a great case for just abandoning a key signature and writing accidentals where needed.