This popular riff is often one of the first an aspiring guitarist learns, as it is easy to play and distinctive. But when I am trying to understand it in terms of music theory, it makes me wonder.

Just the plain tones are G-Bb-C-G-Bb-Db-C-G-Bb-C-Bb-G. But these notes neither fit G major nor G minor (the Db is not part of any of these).

Also what baffles me, there are two ways to "add notes". For example, I mostly find that a fourth note is added to every of the above, like in this tab. But other people add the fifth, like here, i.e. playing power chords (suggesting that chord vary in the riff, but that would neither fit any of the above keys).

So could this be somehow explained theoretically? And why fit both version above?


The two different tabs are the same chords, the first is an "easy" one for beginners, and is correct according to videos of Ritchie Blackmore and Steve Morse. It's an inversion with the 5th as the lower note, and the root an octave high. You can get away without it in the bass position, as your bass guitar provides a strong root (and rhythm) throughout.

The second example is the more normal form of the powerchord, and it has the root note in as the bass as well, which doubles up the octave, so if playing on your own this may be the best way to get a bigger sound.

In terms of chord choice, music doesn't need to remain within any framework, however classic rock is very much grounded in blues scales, and Ritchie Blackmore has long been keen on breaking out of expected musical theory into interesting directions (see any of his later progressive stuff for examples!)

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    To my ears the inverted way isn't just easier, it sounds more like the recording. Maybe I'm wrong. Plus it's hard to tell which is the organ part and which is the quitter part. – Todd Wilcox Apr 12 '17 at 18:07
  • If you look at various videos, it looks like he uses either (or both) - see youtube.com/watch?v=ikGyZh0VbPQ and youtube.com/watch?v=0-DjZXOSUuc – Doktor Mayhem Apr 12 '17 at 18:32
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    although in Steve Morse's video, he describes it as fourths...hmmm – Doktor Mayhem Apr 12 '17 at 18:36
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    From the man himself @ 1:00 mark: youtube.com/watch?v=YzJJgSls5-U he calls them "Rigid Fourths"? – Yorik Apr 12 '17 at 18:49
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    I don't think you are asking what you think you are asking. It's a very straightforward riff around a G blues. Remember many tabs are incorrect (I almost never trust them) – Doktor Mayhem Apr 12 '17 at 18:56

It's basically a power chord riff with the roots following the G blues scale. Rock music is often a mixture of major, minor, blues, and modal tonalities.

Also what baffles me, there are two ways to "add notes".

As Dr Mayhem says, the second tab simply adds another root note an octave below.

  • No more explanation behind that? What scale to use for improvisation or stuff like that? No "tonal system" behind? – StefanH Apr 12 '17 at 18:48
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    Blues allows you to improvise in a number of ways. Ritchie does a lot in a range of modes - if I recall he likes a lot of mixolydian and Dorian. – Doktor Mayhem Apr 12 '17 at 18:58
  • @StefanH G blues would be a good starting point for improvisation over the riff. 'Blues' could be said to be a tonal system, I guess! – topo morto Apr 12 '17 at 23:24

The riff is just (part of) a harmonized blues scale. All melody notes (as correctly shown in your question) are from the G (minor) blues scale:

G Bb C Db D F

The harmony is a fourth below the melody. This can be seen as an inverted power chord (the fifth dropped down one octave), or, equivalently, as the top two notes of a three note power chord (root-fifth-octave).

Many rock guitarists use that form of power chord, especially when the chords change quickly as in riffs similar to 'Smoke On The Water'. Ritchie Blackmore used the same power chords (in fourths) in his riff in the Deep Purple son 'Burn'.

As a final note, it's rock'n'roll, so please don't overanalyze it ...

But now that we're at it, note that in the riff, the fourth under the blue note Db is an Ab, which is not part of the G minor scale or the G blues scale. It can be understood as borrowed from the G phrygian scale. This is not that far-fetched, keeping in mind that the second chord of the chorus is indeed an Ab chord, which is clearly borrowed from G phrygian. It all makes sense, even though it would almost certainly be wrong to believe that the riff and the chorus were "constructed" in that way. This is just a descriptive analysis of how one can try to understand why this works as well as it does.

  • Thanks @Tim, but now I got carried away a bit, and the last paragraph has become the penultimate paragraph :) – Matt L. Apr 13 '17 at 17:10
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    That Ab is only a passing note, very short, so could even be justified as a chromatic! – Tim Apr 13 '17 at 17:34

I'm confused by your statement that B flat is not part of G minor, but let's look at your implied assumption, that the main riff has to contain only notes from the key, e.g. G A B C D E F# for the key of G. As has been pointed out, here you have a flat 3rd and a flat 5th. These blue notes should not be a surprise and without knowing the tune well I'm comfortable assigning it a key of G. If someone prefers they can analyze and say it's a C flat modolygyrian, but a simple tune cries out for a simple explanation.

  • Sorry, yes that was wrong, Bb is part of G minor. Sometimes I make stupid mistakes... – StefanH Apr 12 '17 at 20:50

Agreed: with the G-Blues scale. Additional point on the Db. Flat 5 of G is in blues scale. Also it is common to approach a key note (often a chord tone) from above or below by a half step. You might notice that the Db slides into the C. C is not a chord tone but definitely a target note in the riff.

Probably a bit too much analysis for a classic rock tune! (but I just love jazz theory)


All of the notes of the 'leading voice' are in the Ab major scale:

  • Ab Bb C Db Eb F G Ab

However, the supporting 5th for the G (D natural) is not in that scale, otherwise, all the other supporting 5ths are (F, G and Ab).

So, I would feel comfortable describing this riff as being in the key of Ab major with one accidental.

If you wanted to get a little more technical, you could also describe the riff as being in the key/mode of C Phrygian Dominant, since it seems that the 'tonal center' of the riff is C. The C Phrygian Dominant scale is:

  • C Db E F G Ab Bb C

Again, this would still have the D natural appear as an accidental. I only mention the Phrygian Dominant since it is a common key/mode for Metal guitarists and Deep Purple is often thought of as an early influence on Metal.

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    Keep in mind that "being in the key" of something indicates that that "something" is tonic, a point of rest. It's hard for me to hear Af as a point of rest in this riff (especially since it's never actually played!), whereas G is a clear point of rest. – Richard Apr 13 '17 at 15:49
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    That is why I had mentioned C Phrygian Dominant, since I and the V of that scale, C and G, are the 2 most emphasized notes in that riff. – DougRisk Apr 13 '17 at 16:41

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