and I was wondering if anyone could explain why. I’m specifically curious why the program transposed the G to a Bb instead of a B? I know the source was a flattened 7th in the key of A, but aren’t I asking it to transpose to the nearest diatonic pitch regardless, when it does the transposition?
I am no expert of the area, but my understanding is that it transposes with a diatonic interval, rather then transposing with an interval that will result in a diatonic pitch. In A major, the diatonic third on the 7th degree will be a minor third.
I guess I was presuming if there was a stated key signature (A major in this case) that it would automatically align the transposition such that it could only hit a note actually belong to that key once done. I’m pretty sure this is how Logic does “quantize to key” in it’s Piano Roll so was presuming the same behavior. You also mentioned that in A major, the diatonic third up from the 7th would be a minor third - I’m not sure if I’m following you (but maybe I just need to dust up on my theory terminology )…How would transposing the 7th (in my example it was actually a b7, or G natural) in the key of A) - when transposed up diatonically a 3rd - result in a Bb? (just curious).
Andras is correct that a diatonic third above the 7th degree of A major would be a minor third. In A major the 7th degree is G#, and the B which is a third above would be a minor third. If you’re using G natural in A major, you’re no longer diatonic (belonging to the key), so yes, a minor third above G has to be B flat.
So in other words, “transpose by diatonic 3rd” is retaining the non-diatonic nature of any “source” notes - so the G (b7 in A major) becomes a Bb (b3rd) when transposed diatonically by a 3rd? Still feels to me like transposing “diatonically” would mean “transpose to the nearest note in the diatonic key that you are in” (so even a b7 G note in the key of A when transposed “diatonically” up a 3rd would become a B natural - not flat - in the key of A), but maybe that’s me.This isn’t just being nitpicky of course - conceptually if I’m transposing diatonically (at least in Logic) it’s because I want to quickly find chord tones in the current key I’m in to use as harmony notes, so to me that Bb is a strange choice (even if the source is a b7 “G” note)…
I can see where you’re coming from and why it may seem like odd behavior, but the theory rules are quite strict. A minor third must always be 3 semitones, and there’s no way around that. Likewise, for it to be an interval of a third, the letters must be correct. For example, G to A# is an augmented second rather than a minor third, despite the notes being the same on a keyboard. So to transpose diatonically means to remain within the key. Because a diatonic third above G# in the key of A major must be a B, then if you change the source note (in your case lower it a semitone) then the transposed note must also be lowered by a semitone.