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You can use different combinations of white notes, to give different flavors, open up different harmonies and emotional impacts (bluesy, poignant etc). But the flavor gets very samey, like a hang drum. In that situation (all black notes) it's a pentatonic scale, so any of the 5 notes will sound "right". If you want to write better stuff, learn to play the right notes over each chord (tip - they are the same notes in the chord, and when you get that down, you can play the extensions like 7th 9th 11th.etc).after that you can learn the “wrong” notes to play that can work as well and that will help you write more unique chord progressions. So yeah - all black key chords, just play all black notes over them. I can explain why, but it’s probably confusing. This will also work if you put in F# major pentatonic. If you are super lazy you can just get a riffer or arp plugin and set it to Ebmin pentatonic and let it play over your chord progression and just tweak it. So the 1 -3-5 of that chord - what is it? If you don’t know, its worth learning this stuff. You need to know what notes are in Ebmin and what extensions you can use. Let’s pretend it’s Ebmin, again I have no idea what you did.
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I’m not sure what style of music you make though. When you put first chord down it doesnt mean you are locked in at all.
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Just understanding a few things - the major scale (covers the minor as well), chord arpeggios plus their extensions and then later on, modes will help you grasp all of this really easily. Not saying it’s you, but this is where the “I don’t learn theory man, it ruins my vibe” guys really struggle if they dont have good ears. The circle of fifths is an important companion. No one can really tell you the right way to develop melodies and chords, but practicing a lot doing both makes it easier. Or maybe I come up with some good chord sequence and have to find a melody line that fits. A melody can sound very different depending on the chords around it. Once I've got a few important tones to work around, the chords have to support the phrase somehow, or enrich it. There's no note or chord that can't be led into. Try adding C and F to your black keys scale. It starts to expect what you throw at it. The brain is good at figuring out the context.
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If you start with a richer harmony, the wrong notes don't surprise as much. They can be leading tones for new harmonies as well. But some wrong notes are better than others. Once you establish a scale, some notes become wrong. Nothing's carved in stone but a collection of enough notes becomes a scale, and most of the ones you're used to contain eight of them. Well, good on ya for asking the question.
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