Key signature identification

Hi all, we were having a discussion in our band and it revolved around identifying the correct key for the song “All night long” by Lionel Ritchie. I thought Ab but my guitarist chose Db saying that it is more appropriate as the song in his view is Ab mixolydian. I know your theory is vastly superior to mine. Any help would be much appreciated. Lionel Richie - All Night Long (All Night) - YouTube

Looks like it’s 5 flats - All Night Long (All Night) By Lionel Richie Lionel Richie - Digital Sheet Music For Piano/Vocal/Guitar (Piano Accompaniment) - Download & Print HX.15410 | Sheet Music Plus

Hi Clinton, thanks for replying, I have also seen a horn chart that is written in 4 flats (concert).

I would like to know if there is a theory explanation to suggest which is the preferred way of identifying the key. The tonal centre for me is Ab but there are sufficient accidentals in that key which would not be required if it was written in 5flats.

Hey Cliff,

Theory-wise, you identify the key by the actual key signature, if you have the music in front of you. The key is only one of two possibilities, and that’s either major (in this case Ab Major) or it’s relative natural minor, a sixth up from the root, so F Minor. Generally, you can identify a key signature from a melody, as the melody will most often begin on the key’s root or 5th, though it might be a bit more difficult if the song is using a modal melody.

The accidentals in a key serve a harmonic function normally. If you change the key signature to accommodate them (i.e. to eliminate them) you would be changing the harmony and harmonic functions. If you change your key of Ab major to Db major, your G chord goes from being Gdim to Gb major–a completely different sound and emotional feel.

So if you’ve established a key of Ab major, but suddenly play a Gb major instead of the expected Gdim, you get a specific harmonic feel and function. If you change your key to Db from start and establish that key, the Gb major is the normal chord; you always play that and then lose the emotional pull of the chromatic chord from outside the key.

So the key will be Ab major, but if the harmony is heavily focusing on Db, the song may be trying to give a Db Lydian modal sound. Anyway, that’s the theory :face_with_monocle: :smiley:

Thanks Matt, I’m ok with determining the key from the signature and understand that it can be CMajor or Am for instance. I guess the problem I had was listening to the song, I have to show the horn players what to play. The song opening chords are Ab Gb Bbm Ab. I assumed that as the Ab starts the song and feels home that it was the one chord. But the Gb is not diminished!
So I guess that would point to the key of Dbmajor then?
I have to go now but I’m keen to understand, at the minute these concepts seem vague. I want them to feel intuitive , again thanks for helping.

The key signature is equivalent to Db, but I would say the song is in Ab.
As I listen to the song, for my ears, Ab is absolutely the tonic or “home” chord. What makes it less obvious is the use of the flatted 7 major chord (Gb), which is a fairly common device in music. So just glancing at the sheet music, you see 5 flats (Db), and you see Gb and Ab (the IV and V chords of Db, so you might conclude the song is in Db.
But then you see and hear that the song never resolves to Db; it always resolves to Ab.

If i was just writing out a chord chart, i would say the song is in Ab. But since there’s also sheet music with written notes, the Db key signature provides for the Gb without having to use an accidental every time it appears in a new measure.


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Thanks Steven, that was my thinking too. I play strings and reeds which is how I work out my roots and chords. Either on guitar or keys then I use Finale to arrange it in concert. My guitarist has a great ear and perfect pitch but sometimes guitarists and I include myself can speak in terms of chords over roots (bass) when defining the song content. This often sounds correct when we play but Strict terminology accuracy can be secondary for ear players. We discuss set lists and naturally the keys that the singers require. This is when the discussion about Db or Ab came up. I like to understand any views that query my own so that’s why I came here.

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Right, Ok so then if the notated key signature is Db major/Bb minor, but you keep resolving to Ab as the tonic, you’re playing with a modal harmony, in this case Ab Mixolydian, since Ab is the V of Db major. And really, the only difference between Ab maj and Ab Mixolydian is the bVII or Gbmaj vs Gdim.

I think to be fair then it sounds like my guitarist is correct. It has an Ab mixolydian melody and resolves to the V of Db. Even as I write that it sounds weird! I have only ever written in the major or minor key. Never thought about notating for the modal scale which identifies the melody. I’m still coming to terms with this revelation. Of I’m brutally honest I still feel that notating in Ab makes the most sense despite the lack of the Gdim chord. I have seen lots of songs with in CMajor with Bbmajor chord giving that typical harmonic pull but I’ve never thought that it was not in CMajor.

Can’t figure out how to format this notation, so I’ll just say:
If I was using chords for the chorus, they would be Gb Ab Gb Ab…

If I was using roman numerals, they would be bVII I bVII I…


It’s still not formatting how I want, but hopefully you get the idea…

Yes, that makes the most sense to me.