I am writing a music piece in E minor using the chord progression Em-C-Bm-G.
I independently wrote an arpeggio in the chord e minor (together with some passing notes) and I want to add this arpeggio to the song over the chord progression.
My question is, am I allowed to do this?
The arpeggio continuously plays in E minor while the chords in the progression change.
Should I adapt the arpeggio on the progression?
The arpeggio continuously plays in E minor while the chords in the progression change.
Should I adapt the arpeggio on the progression?
Music is art. You can do whatever you want.
But, it seems clear to me you are trying understand some basic harmony concepts like combining chord tones and non-chord tone to follow a harmonic template (chord progression.) You're trying to learn about musical conventions.
Two concepts that you should look into are pedal points and ostinato.
A pedal point is when a single tone is held for a long time while harmony in other voices continues to change, and importantly, some of the continuing harmony deliberately clashes with the pedal tone! Usually the changing harmonies return to match the pedal tone, and the commonest pedal tones in tonal music are the dominant and tonic. From a certain "high level" analysis the harmony of a pedal is just an elaboration of a dominant or tonic chord where the whole passage can be analyzed as either V or I.
The connection between your idea to a pedal is that you have one thing - the E minor chord - being held while the other parts move against it. You have a sort of "pedal chord." If your chord progression came back to E minor, like Em-C-B-G-Em or something similar, it would be following the concept of a pedal but with more dissonance from multiple clashing tones.
You can generalize this idea even further. You mentioned that your E minor arpeggio uses passing tones. The super high level concept is the ebb and flow of consonance to dissonance to consonance, stability to instability to stability. Passing tones, pedal points, tonic to dominant to tonic, etc. exhibit this idea. It's a basic fundamental of tonal harmony.
Ostinato is when a fairly short melody idea is repeated over and over. If your E minor arpeggio not only holds the chord, but also repeats a short figure, it would be an ostinato.
You are allowed to do exactly what you like in music! As long as no-one gets hurt.
There are many people like yourself who think there is a set of rules that must be followed. Please rid yourself of that notion. A lot of those 'rules' came about through certain things seeming to work well, but they're guidelines rather than rules.
It's your music, you can do what you like with it. If others like it, all well and good - if not, then there's your answer, sort of.
Now to the question! Usually, what sounds best is a change of notes when there's a change of chord. Otherwise there will be clashes. Sometimes, not always. Obviously the Em arp. works over Em. Then comes a C chord. Along with the Em arp., it can work, as it will produce not a straight C chord, but a Cmaj7, which sounds fine in that place.
The Bm chord that follows has B, D, F♯ in its make-up. None are the same as E, G, B from Em. So there will be clashes there. The chord G has G and B, so against the Em arp. will make a G6, again, fine.
