I'm writing a backing vocal for an already-recorded song. Since there are other melodic parts she'll be singing over, I'm going to give the singer a score to work from.
In this case, the singer will be singing oohs and aahs in between the verses of the song. Providing pitch information is no problem, but how much should I write in terms of what vowel sounds to make?
Should I write in suggested oohs and aahs or leave it open for her to improvise? What methods of conveying this exist already?
It depends on the kind of sound that you're looking for.
If you need / want really specifically placed vocables, then you would notate the pitch, rhythm, and exact measure / beat among other info. If you don't care or it doesn't matter, then just give her the pitches for reference and let her go to town (read: using instinct). If you'd like her to improvise but she doesn't feel very comfortable doing so, then writing suggestions in the score would be a good framework for her to work from - like a security blanket.
To notate:
Simply write what you'd like to say just like you would any other lyric. I know it might feel silly to write "Ooh" and/or "Aah" but they'll know what you mean and you'll get the effect you want. Don't write "Oooooooohhhhhhhh" for longer notes - just show the rhythm; they'll sing it correctly automatically.
Good luck!
If you want to write out pitches/duration/etc, go ahead and do so as you would any melody or harmony line, including breaks, breaths, and rhythms. Writing "Ah——" for lyrics is perfectly acceptable!
It's also perfectly acceptable to both give written music to a vocalist and ask them if they'd like to improvise instead. Some like to, some don't. The written music may serve as base for improvisation, and is also somewhere that the vocalist can write down ideas, changes, and clarifications.
