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According to The Most Popular Keys of All Music on Spotify, an analysis of their song library, sharp keys are more common than flat keys.

the keys distribution of all music on Spotify

Why?

41

It's an artifact of Spotify's analysis. Notice that this chart shows no songs written in a flat key. Therefore, without a doubt, the chart is simply using "F♯" to mean "F♯ or G♭," "A♯" to mean "A♯ or B♭," and so forth.

In particular, B♭ major (with a key signature of ♭♭ – two flats) is definitely much more common than A♯ (with a key signature of 𝄪𝄪𝄪♯♯♯♯ – ten sharps, which is to say, three double sharps and four single sharps). But the chart shows B♭ as though it were A♯.

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    But (without disagreeing) it's correctly identified F major (1 flat) and C minor (3 flats), but loses the plot after that. Dodgy data! – Steve Mansfield Oct 17 at 18:35
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    +1, exactly. No way are 2% of all songs written in D# major. – Kilian Foth Oct 18 at 7:21
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    @SteveMansfield It's the name of the key this answer is referring to, not its accidentals. This is another example of Bad Data resulting from Non-Experts trying to do "analysis". Musicians know that, say, the key of A-flat is not the same as the key of G-sharp, especially on string instruments. The tuning (bending) of notes is different, for just one thing. – Jeff Y Oct 18 at 13:44
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    @JeffY: The data would be fine if it were labeled as identifying the key-note pitches and primary tonality of music, rather than the keys. Most likely Spotify is determining key-note pitches via audio analysis, and would recognize a piece of music in Db major, as having a key-note pitch of C#. Using sharps consistently makes clear that it is not trying to make any distinctions between enharmonically-equivalent keys. – supercat Oct 18 at 15:09
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    @JeffY: Spotify is a recorded-music service, rather than a printed music service, and the meaning of "key" is different in the two kinds of music. If Spotify has an option to identify a recording that starts in the same key as another one ends, such an option would classify music by key-note pitch; I would guess the chart is a display of data that was produced for that kind of purpose, rather than for the purpose of identifying keys. As for why C, G, and D are so popular, it's because a standard-tuned guitar can play C, G, D, Dm, A, Am, E, Em, and B7 (but not B triad) open chords. – supercat Oct 19 at 18:13
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While there are certainly questions about how all of this data was classified, it's not surprising to me that the most popular keys tend slightly toward the sharp side (G, D, and A), with flat keys like F and B-flat ("A-sharp") turning up with smaller percentages.

I assume much of Spotify's catalog is popular music. Guitars and electric basses are rather dominant instruments there, which tend to be biased slightly toward sharp keys like G, D, and A in their typical tunings. (That is, it is often somewhat easier for beginners to play the basic notes and chords in these keys, due to more open strings and the use of only the first few frets.) Obviously keys near to C major on the circle of fifths are also relatively easy to play on piano/keyboard, another central instrument in pop music.

That leaves the mystery of why C#/D-flat and G#/A-flat are also ranked somewhat highly after the central keys of C, G, D, and A. My immediate question is how Spotify determined the key for songs that have more than one key. If they looked at the final key, many pop songs contain a final modulation that moves up by a half step, which would take C and G to D-flat and A-flat. That's speculation, but one potential explanation. (Of course, I'm putting a lot of faith that Spotify's key-finding algorithm is accurate, which it may not be.)

But why the most popular keys tend toward the slightly sharper side seems clear: they work reasonably well on both guitar and piano.

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    Very true - if you were to limit the search to, say, classical music, you'd find that key signatures with more than 3-4 sharps or flats were very rare. (Before equal temperament became the standard, such keys would have sounded very discordant on many instruments.) – Darrel Hoffman Oct 18 at 14:14
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    Possibly D-flat and A-flat are the result of bands that tune down a half step. – wrschneider Oct 18 at 14:27
  • Exactly. You might add a contrast with brass instruments, which tend to be more comfortable in the flat keys, but are less common than guitars in pop music. – Greg Martin Oct 20 at 19:42
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Simple answer - they've labelled keys in an unusual manner. G♯ is normally written as A♭; A♯ more often as B♭. That's for starters. Redefine in the more commonly used key names, and the proportions change.

At least it's not like some guitar sites, which eschew flats altogether, and only live in a world of sharps!

4

To answer the question posed in the title, I have noticed three things that gently influence the choice of key.

  • Transposing instruments For long-forgotten historical reasons, transposing instruments are in flat keys (e.g. Horn in F, trumpet in B flat, Sax in E flat). I have seen a few odd instruments in G and D, but flat keys are the norm. This means that if the C instruments are in E major (4 sharps), the trumpets are in F# major with 6 sharps and the Eb Sax will be in C# major with seven sharps. I suspect the average composer will soon decide to raise the whole piece by a semitone to put everyone into more reasonable keys. The effect is to make the flat keys slightly more preferable.
  • Stringed instruments Sharps are always the next position up the fingerboard from the natural note. In contrast, Eb, Ab and Db on the violin are on the string below the natural note. Not a biggie for the experienced player, but a difficulty for the learner.
  • Sharp keys sound brighter There is a school of thought that says sharp keys sound bright and flat keys somewhat dark. This question has a long discussion on the topic.

I don't have authoritative sources to confirm this - it is just my opinion.

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    While your latter two points are certainly influences, the first point actually works against the sharp key theory. Wind ensemble and band pieces are often written in flat keys specifically because of the common transposing instruments. E.g., a piece in B-flat will have trumpets reading in C and alto saxes reading in G, but a piece in, say, D major will have trumpets in E (4 sharps) and saxes in B (five sharps). – Athanasius Oct 18 at 0:48
  • "Sharp keys sound brighter": so does the key of F# sound really bright and Gb really dark? – PiedPiper Oct 18 at 16:25
  • So sharp keys sound brighter simply because they're higher notes? – Randy Zeitman Oct 18 at 20:23
  • @Athanasius Thanks for the correction - I've edited the answer – kiwiron Oct 18 at 23:05
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Firstly, the data is presented in such a way that it is difficult to see if what they are alleging is true. Secondly, they have no key signatures with flats in their names. I'll give them a pass on six sharps (though this could be just as well written as six flats) but A# major is ridiculous.

I've tabulated the data below. it totals up to 99.8%. I'm not sure if that's my maths or their rounding error. I've totalled up the cases for up to 5 sharps or flats. The cases 0 sharps/flats and 6 sharps/flats do not belong to either the sharp key or flat key category.

For minor keys there is a bias toward sharp keys 14.2% vs flat keys 13.8% but this is vanishingly small. For major keys there is a bias toward sharp keys 31.7% vs flat keys 21.5%. Removing G major (10.7%) from the analysis would cancel this difference, so we can say that on average music written in a major key contains on average about 1/2 a sharp.


5b        Bbm* 3.2%   Dbmaj*  6.0%
4b        Fm   3.0%   Abmaj*  4.3%   
3b        Cm   2.4%   Ebmaj*  2.4%   
2b        Gm   2.6%   Bbmaj*  3.5%
1b        Dm   2.6%   Fmaj    5.3%
TOTAL b       13.8%          21.5%

Natural   Am   4.8%   Cmaj   10.2%

1#        Em   4.2%   Gmaj   10.7% 
2#        Bm   4.2%   Dmaj    8.7%
3#        F#m  2.5%   Amaj    6.1%
4#        C#m  2.1%   Emaj    3.6% 
5#        G#m  1.2%   Bmaj    2.6%
TOTAL #       14.2%          31.7%

6#        D#m  0.9%   F#maj   2.7%

GRAND TOTAL   33.7%          66.1%   

Keys marked with a * are shown as sharp keys in the original data, 
but are better and more commonly written as flat keys.

The bias is, as noted in the article itself, probably due to the instruments used. Older music with wind and brass may favour flat keys, but Spotify will contain a lot of guitar music, and guitar is a little easier to play in sharp keys, particularly in major.

On guitar Amaj, Emaj and Dmaj are among the easiest chords to play. The Relative minors F#m, C#m and Bm are all barre chords however. I think this explains why the bias towards sharp keys occurs only in major but not in minor. For playing in Am/Cmaj the chords Am, Em and Dm are also easy, and there are other easy chord shapes for Cmaj and Gmaj (but Fmaj requires a barre, which can be avoided by playing in the key of Gmaj instead of Cmaj.) There are many songs written for guitar that only work with open string chords, not barre chords, and therefore often can only be played as intended in the key of Gmaj or Amaj for example.

  • It looks like their rounding error. I added them their numbers and also got 99.8%. – dan04 Oct 19 at 6:20
  • Good answer, +1. This whole thing is not even a storm in a teacup. – Tim Oct 20 at 16:58
  • Surprised this isn't voted higher. It's the only answer that attempts to numerically quantify the "real" sharp/flat key distribution. – dan04 Oct 20 at 21:27
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In many contexts which describe audio pitches, it is common to use the names "C C# D D# E F F# G G# A A# B" [except in German, where the last three notes would be "A B H"]. The chart is most likely produced by processing the songs, identifying the apparent key note and primary tonality, and then determining the pitch of the key note using the above names. Listening to a piece of music, it would be impossible to distinguish between B and Cb, F# and Gb, or C# and Db, or between the associated pairs of relative minor keys. Using A# to refer to Bb may seem unusual, but it helps to make clear that the chart is only identifying the audio pitches associated with the key notes, rather than making any judgment as to how they are written.

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Aside from the notational issue of "no flat keys," the data as presented isn't consistent with common sense.

There are only a handful of classical pieces in D sharp minor in the entire repertoire (I challenge anyone to name more than five), and nobody is likely to write anything for guitar in either D sharp or E flat minor, so Spotify's claim that almost 1 in 100 pieces is in that key is simply unbelievable.

More likely, there are about 1 in 100 pieces that are in either D minor or E minor, but were not played at A=440 pitch, and Spotify's software mislabelled them.

Since there is no reason to believe the other groups are any more accurate, the whole chart is a work of fiction unless somebody can prove otherwise.

  • 1
    There’s a big difference between “their analysis was a bit crude and the presentation misleading” (which, as you say, it clearly was) and “the whole chart is a work of fiction”. Exactly as you say, it’s pretty clear what their analysis actually did — they identified the tonic pitch somehow, and labelled that pitch assuming A440 equal temperament (and classified as major/minor somehow). Crude, but it still tells us something meaningful. – PLL Oct 19 at 16:54
  • @PLL - the meaningful thing it tells us is that if you don't know what you're doing, it's best to leave it alone! – Tim Oct 20 at 16:59

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