Note: I am not that good in general music theory but I will try to get my point across as best as I can.
I am currently in charge of writing/transposing the scores of a little hobby band.
I got the scores written for singing and now I need to transpose it for an Alto-Saxophone. The singing has one ♭ so it is either D-Minor or F-Major.
What accidentals (I hope that is the right word) do I have to use when rewriting it for Saxophone and where can I look up which instruments have what signature?
Your voice part's key signature has one flat. The corresponding alto saxophone key signature will have two sharps.
Voice is written in what is called "concert pitch". Concert pitch means that when you write an "A" (specifically, the "A" above "middle C") it is tuned to 440Hz. Instruments like voice, piano, and flute — so-called "C instruments" — are all written in concert pitch.
The alto saxophone is an "Eb instrument". This means that its written music and the "concert pitch" sound that results are not the same. When "C" is written in an alto saxophone part, the resulting concert pitch — the note a singer would sing to match the alto saxophone's "C" — is the Eb below.
Put another way, concert pitch — the actual sound produced in response to a written saxophone part — is a "major sixth" lower than the written note. And to produce a given concert pitch, the saxophone part must be written a major sixth higher.
Thus: D minor / F major becomes B minor / D major.
The alto sax part needs to be written in the key of D Major (2 sharps). The alto transposes, and It's sounding pitch is a major sixth below its written pitch. When the vocals sing do-re-mi in F (notes F-G-A), the alto player must see this in D. He/she will read D-E-F# and they will sound in F major. To verify this, look at any concert band score. The altos will always have three sharps more/three flats less than the flutes, which are in the "concert key."
Look at this score, in Bb with altos showing key of G.
Aaron's answer is correct. To simplify any future writing, the simple formula for E♭ alto is to add 3 sharps to the existing key signature. That's what happens writing for concert F major - add 3 sharps to become D major.
So, if the original concert key is 1 sharp, adding 3 sharps will take the key to that of 4 sharps. Original key 4 flats becomes 1 flat (adding a sharp = subtracting a flat).
If you are going to do this a lot, I strongly suggest you shell out the cash for a music writing software. I won't recommend one, I haven't done this for years.
A good one can scan your sheet music, then you can grab the notes with the mouse and transpose them by just pushing, or use the built in functions. You still have to adjust it by hand, but it will save you an awful lot of time, and it also formats and prints the music nicely for you.
It is not too much money, and I see the licence for mine is still valid, so it gets updated now and then.
