dopemcee said:
say for example i im working with the A flat major scale to do the bassline.. does EVERYthing else that i add to make that beat complete have to be done with the keys that make up the A flat major scale(and its relative minor)?
No. You can play any note you want. You just have to be consious where you play them. Any note played that's not diatonic to the key of the song is called a color or passing tone.
Nothing is off limits, but if you avoid ending your phrases with color/passing tones, and avoid playing those color tones on the strong beats, it will be easier to make them sound good.
So, for example, if your song is in Ab(Ab-Bb-C-Db-Eb-F-G), you can sneak a 'B' note(minro 3rd) in to add a bluesy flavor, but keep it off the downbeats and off the end of the phrase.
dopemcee said:
sometimes i wanna add other keys but im sort of limited cuz it always sounds outta place.
It's all about timing and placement. Try playing that 'B' note against an Ab chord like I explained above. In addition to the things I said avoid, don't lean on the note for to long and play it between two chord tones.
Let's say your tune has a strong back beat, hiting hard with the snare on the 2nd and 4th beats. Play the 'Ab' on the first beat of the measure. Play the 'B' on the
and of the first beat. Then resolve that short phrase with a 'C' on the 2nd beat. For an example of how this can sound great, listen to any blues tune.
The example I'm giving is the simplest, most basic way to add a color tone to your melody. Once you get the hang of it, you can play them almost anywhere you want if you resolve the phrase with a scale or chord tone.