The key of any piece of music can have a big impact on the final sound.
I am not talking about the scale, because obviously that will matter the most (example: major vs minor). I am talking about the root key of the composition.
The key of the music changes the overall dark/bright levels (try transposing a piece up or down a few tones). But most importantly, the key of the music changes how the every instrument and vocal can deliver all the lines.
There is something called “Tessitura” in music, which is basically the comfortable range of a voice (or instrument) where it sounds best. So let’s say you have a vocal range from C3 to C5.
You will always have worse control and tone in the extremes of your range, so the first lowest notes and the highest ones will be outside of your Tessitura.
Instruments can also have a Tessitura range, where the lowest notes can be too soft, perhaps raspy and brittle. And the highest notes can sound strained and pitchy.
Now, what does all this mean for answering the main question?
How to Choose a Key for Your Song
- First make sure the Key suits the Leading Voice (if there are vocals)
- Choose a Key that suits the tuning of the Main Instruments
- Generally avoid keys with too many sharps/flats (hard to read)
Sometimes you want to flip this perspective though, if you are a mainly a music composer like myself, and choose the vocalist or instruments depending on the key you have written your music in.
As a composer I mainly compose on the piano keyboard, so the Tessitura or instrument range is not really applicable, everything will sound good on the piano.
Let’s say I write the music in G minor. And let’s say the melody goes below the root (G) to F as the lowest note, and up to Bb on octave above at the highest.
After I finished composing the song, I can look for a vocalist (if I want vocals) that suits that key and overall melodic range. And I can also choose instruments that will suit the same key (and range).