How to determine if a song is in F#Aeolian or D Lydian or Ab Locrian

Question

Hello how are you? :) delighted to be here in my first post, I am a graduate of Sound Engineering and I am currently studying modern harmony in a self-taught way, I have been able to understand the bases of harmony with the help of some books I bought. I also study songs and try to determine the key they are in so that I can understand harmony and melody.

A day ago I listened to the musical group Frou Frou and I loved the use of their arrangements and vocal melodies, there is a new song called "A new kind of love" and analyzing the melody I came to the first conclusion that it was in G# /Ab Locrian, this simply by determining the notes that the voice sang, as these also belong to several other scales, for example, F# Aeolian, or D Lydian, or A Major which would be the source scale, how can I know how they approach the harmony and melody? ie from A Ionian or D Lydian etc? the keyboards play at the beginning a C#m7 and F#m7 in cluster voicing and at the beginning of the verse the bass makes a progression from D E F# A and this makes me feel that the rest falls in D. Am I right?

I saw a page (Hook Theory) that mentioned that the song was in F# Aeolian but for some reason I don't feel the rest in F#,

That is why I approach you to know how I can interpret this and we can also talk about the harmony of this group which, in this song, there is a lot of use of clusters and a maintenance of chords that look good in the progression of the verse, for example the C# note that is present throughout the verse,

I look forward to your answers, thank you very much

Answer 1

It all sounds pretty well in A to me - albeit a rather out of tune A. The bass is landing on that A very frequently.

Incidentally, had it been A♭ Locrian (it certainly isn't), since it's from parent key A, we'd call it G♯ Locrian. Key A has G♯, not A♭.

Songs and other musical pieces will often 'stray' into other modes, and even into parallel keys, so it's nothing out of the ordinary. The place any piece feels like 'home' will be what we determine as the key. At very least, the key signature will be 3♯ for my money!.

Answer 2

It's understandable that one would hear D as being the tonic — the rest point. It is the starting point of the chord progression, thus very prominent to the ear, and the A at the end of the progression is the harmonic return to D, thus reinforcing it.

However, F# is the true target. The way to hear this is to listen to the way the lyrics in the verse aim toward that point where the bass in on the F#. Every time the vocals pause on a long note (i.e., sustain a lyric longer than the others), the bass is at F#. Put another way, every vocal cadence (or "mini-cadence") in the verse occurs on a bass F#.