How to choose a key signature for a song that modulates often?

Question

In jazz, let's say, how would one choose a key signature for writing a lead sheet for a song where keys change every few measures or faster? Is writing the key changes explicitly going to be helpful or distracting? And if it isn't helpful, should you just choose C, and just label accidentals as they come up? What's best for a player to read?

Answer 1

Hi! How are you today? I hope you're staying safe at home!

There's no such thing as a "fixed key" in jazz. Jazz and Blues are not TONAL music, they are MODAL music. This is, arriving to the I degree chord of the underlying key is not the "goal". Even when the song starts and ends in that chord, you will find lots of inner chord progressions (ii-V-I 's , for example) where the "I" is not the key you see at the key signature. The "key changes" in jazz chord progressions are built using resources like changes of species/harmonic functions of certain chords to redirect the progression to a different set of chords. Free use of chromatic harmony and melody is also a central feature in this music.

If you are interested in having some jazz harmony lessons please let me know!

Have a great weekend

Carlos

Answer 2

Use accidentals as opposed to key sig changes, it will be much easier for players to read. Most tunes I've seen that have frequent modulations/use multi-tonic systems keep the same key sig throughout (typically C, even if the tune is never in C) and only use accidentals. Examples I can think of include Giant Steps, Elucidation (Pat Metheny), and All the Things You Are.