Sort of key change effect, can technically explain the effect?

Question

So I'm playing a melody ( synth with a daw ) in D minor key but actually this very simple melody ( mostly made interesting by delay effects on it ) does not touch any note of the key to "prove" it is D minor, since it is playing just white notes.It has a very well defined rest on the D note anyway. When the bass line enter, I used a melody playing between D and C and at that point the whole sound has some weird, but actually pleasant effect. Is there some theory to justify that effect? I some kind of modulation I'm doing between D and C major? This should not be the case because the melody itself sound "minor" even after the bass. Please forgive my ignorance.

Answer 1

I'm guessing you're in what's known as D Dorian. D Dorian uses all the notes of parent key C major, but roots (tonic, home) on note D.

Answer 2

this very simple melody ( mostly made interesting by delay effects on it ) does not touch any note of the key to "prove" it is D minor, since it is playing just white notes.

There are three classic types of minor scale. Harmonic, Melodic and Natural. And today we often extend 'D minor' to include any scale based on D which includes the minor 3rd, F. (If it included the major 3rd, F♯, it could be called a Major scale/mode.

Even if we stick to the strict terminology, the first 5 notes of D Harmonic, Melodic and Natural minor scale are D, E, F, G, A. All white notes (6 and 7 are up for grabs). So you can't really say that playing all white notes fails to "touch any note" of D minor!

If we allow the wider definition, 'all the white notes' starting on D form the D Dorian scale, a very common 'minor' scale type in today's music. We can argue over whether a 'mode' is a 'key', but I don't think that's the issue here?