Here’s how I do things like this and I’m not saying this is the only way or the best way.
We know A Dorian is the Dorian Mode of G Major, so begin with the G Major Scale. Or you may use the A Dorian Mode. Both will give you diatonic chords for the mode. As you may know, A Dorian and G Major share the same basic chords but the function of those chords is different.
For exact chord vocings, even with Scalers’s’ tremendous resources which I use, I find it easiest to simply put basic chords on pads and then Edit those for exact voicing.
At times Scaler’s naming conventions provide synonymous names for chords, e.g., I call a chord C7b9 but Scaler names it Bb Diminished, etc. In other cases I find no reason for Scaler naming things as it does. I’m not sure this part of the program is totally bug free.
At times no matter what I do Scaler will not accept the names I choose. I had an F7 and Scaler insisted on calling it as if Eb was root no matter which scales I used including Bb Major. I bug-reported about that one but have not heard any answer about it.
Anyway, as long as the notes I want are played I really don’t care what Scaler names the chord. I’ve never not been able to make Scaler play the notes I’ve assigned with Chord Edit.
Good luck and perhaps others will have better ideas for you.
So to summarise a bIII is simply the minor chord and in your progression you are replacing the major third of the Dorian with the minor third.
However, the progression you have suggested, I-biii-IV, is not in the Dorian scale as the root chord of A Dorian is A min; but I am assuming this is a typo and you meant i-biii-IV. If you meant a progression of I-iii-IV from a scale with a root of A you are referring to chords in the A major scale.
I somehow thought that you could take any of those progressions and apply them across any key/mode. So, for example I-bIII-IV, in A Dorian I wanted to know what i-bIII-IV would be: Amin-???-Dmaj (in other words, what is the flat degree of Cmaj?). It seems like in the Prog Machine example, they just flat the first and third notes of the chord. If I do that to Cmaj, I think i get Bsus4, but I don’t know if that’s correct because I don’t know if that is a general rule to get a “flat degree” (per the explanation on the Prog Machine app).
Regardless, thanks for the tutorial! I was playing around with that and still got some nice sounds.
I agree about the coolness of the progressions. However, the post you quote says “In C Key the III Chord is Dm!” That’s wrong. E Minor is the iii-chord of C Major and we usually don’t say “C Key” we say “Key OF C Major.”
The Roman Numeral chord/sale naming is useful because any pattern will work in any key. Occasionally a singer may ask for a non-standard key for the song. "Can you play “All the Things in A?” Here’s where Roman numbers help quickly transpose the song. Thinking “vi, ii, V, I” in A Major rather than Ab Major makes transposing easier.
Also when using Roman Numerals for Chords/Scales the Standard Convention is "lower case letters for Minor Chords, upper case letters for Major Chords – I, ii, iii, IV, V, vi, vii for a major key.
How it sounds is what matters and all these naming conventions are all after-the-fact observations and traditions. As Nadia Boulanger said, "to learn music you first learn the rules, but to compose music you learn to break them.
Music is an invisible art form that exists mostly in memory.