What does it mean when we say: ‘The concert key of this piece is Ab?’ It means that the piece is composed in Ab for the C-instruments. It’s not so easy to explain, but I’ll try.
In most orchestras we have mainly C-, Bb- and Eb-instruments.
C-instruments: piano, violins, flute, guitar, bass, guitar, keyboard.
When you play a c on a C-instrument, it sounds like a c on the piano.
Bb-instruments: tenor sax , soprano sax, trumpet, trombone, clarinet.
When you play a c on a Bb-instrument, it sounds like a b-flat on the piano.
Eb-instruments: alto sax and baritone saxophone.
When you play a c on an Eb-instrument, it sounds like an e-flat on the piano.
You hardly ever need this knowledge, so If you don’t fully understand this, then don’t bother. If you play from sheet music, it is normally already ‘converted’.
I played in bands for years without knowing anything about keys and chords. I usually played by ear. And I still do most of the time, even though I know quite a bit about the theory by now.
TIP:
So you don’t necessarily have to understand this, especially since it is almost always calculated and written out for you. But it is good to be less dependent on others and to be able to convert it yourself. If you’re in a pop or jazz band, no one will help you with it; often because they don’t know either how it works.
TIP:
You can see I used lowercase and uppercase letters. It’s generally agreed that we use lowercase letters for single notes and uppercase letters for chords and keys.