My question relates to playing a song with chords. Why would I want to shift a key up or down when I can just play a song in its original key with higher or lower sounding chord voicings? I also understand that if I'm playing open chords on a guitar and shift up or down a key and play its open chords that it won't necessarily sound higher or lower because the voicings are different. For instance, if I play the open chords of I,IV, and V in one key, then shift to another key and play its open chords, the song basically sounds the same because the chord progressions are the same, so why would it matter what key I'm playing in if it's not gonna shift the same voicing up higher or lower? Why would you change a songs key if you're not going to use the same chord voicings of the original key? And why shift key when you can play higher sounding voicings of the same chord? Is the answer because each different major key has a different mood?
Choosing another key is a different operation from choosing other voicings in the same key, or playing the same stuff an octave higher or lower. It's useful to know how to do both things.
Some reasons to try another key:
- When playing with a singer, or when you're singing: A song that is difficult to sing in one key might be easy and/or sound better for the singer's voice in another key.
- For effect: You might just find that a piece sounds better in a different key
- For ease of playing: A particular tune might just lay really well on your instrument in another key.
- For variety - in playing a bunch of songs, listeners might get bored if all the songs are in the same key. In that case you can consider putting some of the songs into different keys for variety.
- It's also sometimes useful to be able to modulate to another key within a tune for effect. This can be built into a tune or it can be an arrangement technique. It can be used to create additional interest or excitement.
- A lot of jazz and classical music pieces will move through two or more keys. Again, this tends to make things more interesting.
Some reasons to try other chord voicings:
- For less awkward fingerings
- For better voice leading
- To make things sound different or more interesting.
Regardless of the chord voicings you use in a song, the underlying melody will be the same if you keep it in the same key. Regardless of the chord voicings you use, the underlying melody will be higher (octave shifts notwithstanding) if you play the song in a higher key and lower if you play the song in a lower key.
The chords by themselves without the melody may sound lower or higher depending on the chord voicings. But if you try to sing or play lower or higher melody notes over the same chord - it will not work (unless you go lower or higher by one whole octave) You still use the same exact melody notes in the song - regardless of chord voicing. If not, the chords won't go with the melody. You can't just randomly pick any I or IV or V chord and sing or play melody notes in any key you want and expect it to work!
So if the song is in the key of G, the part of the melody that is played or sung when a G chord is being sung, will be the same exact notes (not higher or lower) whether you play an open G in 1st position, or a G barre chord on the tenth fret. The chord voicing will sound higher - but the melody notes that the singer sings are exactly the same. Of course you could sing the melody notes an octave or two higher (if you had the range) but you could do that regardless of what voicing of the chord you were singing over.
In any given song, the melody (notes that are sung if the song has words) and harmony (chords) work together to create the essence and feel of the song. If you want to sing a song a few steps higher or lower, you will have to change the key. If you change key, all the chords will change accordingly. Different voicings may serve you will if you want to sing the melody a whole octave higher or lower - but the notes will still be the same (only one octave higher or lower).