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What is the altered scale?

The altered scale is the seventh mode the melodic minor scale. So, for example, C melodic minor is C, D, Eb, F, G, A, B, and the seventh mode is B altered - B, C, D, Eb, F, G, A. Thus you can build any altered scale from the melodic minor one half tone above it.

For those of you who want it served on a platter, in whole tone, half tone build, it is: H, W, H, W, W, W.

The altered scale, used in jazz, is played on dominant 7th chords, and has been a prominent dominant 7th chord sound since the invention of bebop. It is quite a difficult sound to master, as it is very tense, having many strong tensions, but we'll get to that in a second.

Why is it called 'altered scale'?

The altered scale also goes under the name of 'diminished whole tone scale.' As you can see, the first five notes are identical to the symmetric diminished scale, and the last four are identical to the whole tone scale. So the scale starts off as a diminshed scale and ends up as a whole tone scale, hence the name. However, the more common name for it is the altered scale.

Let us take a look at a C altered scale: C, Db, Eb, E, F#, G#, Bb. It has an anomaly - it has both a major and a minor third. This is very uncommon, and for a good reason - a chord is either major or minor, it can't be both. For acoustic reasons, the major third is stronger, and so the chord defined by this scale is major. Furthermore, it has a Bb, i.e. a natural seventh, meaning that the chord will be a C7 chord, i.e. a dominant 7th chord. The 3rd and 7th are the most important notes in a scale, and they do, in fact, define the chord.

So now we know that the altered scale is played over dominant 7th chords. But other than the necessary 3 notes (root, 3rd, 7th), it has nothing in common with the mixolydian scale, which we would normally associate with 7th chords. Compare:

C mixolydian - C,   D   , E, F, G, A, Bb, C
C altered    - C, Db, D#, E, F#, G#,  Bb, C
I've taken the liberty of changing Eb written above to D#, which is the same, but shows clearly now that it is not a minor third from C, but in fact an augmented second. So we see that except for the root, 3rd and 7th, every other note has been altered! Instead of a 9th (D), we have a b9 (Db) and a #9 (D#). Instead of an 11th, we have a #11 (F#). Instead of a 5th, we have a #5 (G#). Many people say that the F# is actually a Gb, so that we have a b9, #9, b5 and #5.

So, as you can see, the altered scale is like the mixolydian scale altered in every possible way!

How do I know when to play it?

Firstly, you can play it whenever you want to, as long as it sounds good. Charlie Parker used this on dominant 7th chords in many situations, and so have many players after him. Let us split it up into two cases:

1) How can I tell when the composer of a piece wants me to play the altered scale?

Simple. If the composer wishes the chord to specifically be an altered 7th chord, he will mark it as one of the following: C7alt (today very common, as all jazz players are familiar with the term), C7#9#5 (also common, as the #9 and #5 are ditinguishing characeristics). Also, C7#9 implies the altered scale.

C7b9 implies the symmetric dimished scale. Why? Convention, I guess. Both the symmetric diminished and the altered scales have a #9 and a b9, but the #9 implies the altered, and b9 implies the symmetric diminished. In C altered, we have an Ab (aka G#), which is also the b13, but chords marked with b13 do not imply the altered scale. b13 usually implies the 5th mode of the melodic minor scale. b9b13 implies the fifth mode of the harmonic minor scale (aka mixolydian b9 b13). b5, even though it is found in the altered scale, usually implies the whole tone scale.

2) When else can I play the altered scale?

Well, basically, you can play the altered scale whenever you want on a dominant 7th chord. You must be wary, though. The altered scale has a very tense sound, because of its strong tensions. Because it has a b9 and a 'b13', it sounds good on seventh chords which resolve to a minor chord. So in a minor II-V-I progression, this might be an ideal time to use it on the 'V' (of course, you can also use the more obvious mixolydian b9 b13 scale, or any of several others, but we're focusing on the altered here.) Thus, you can also use it on a II-V-I resolving to a major chord. Basically, you should be careful, especially as many times the pianist (for example), may play a nice mixolydian voicing, while you play the altered scale, which may be quite dissonant. It's not necessarily 'wrong', but it might not be what you wanted. So basically, you have to be aware of these things.

It is interesting to note that an altered scale is the same as that of a lydian b7 a tritone apart. The altered is the seventh mode of the melodic minor scale, while the lydian b7 is the fourth mode of the melodic minor. So, for example, in F melodic minor, we have E altered and Bb lydian b7. Looking at the notes:

E altered    - E, F, G, Ab, Bb, C, D
Bb lydian b7 - Bb, C, D, E, F, G, Ab
The same. So you can see that you can play an E altered over a Bb7 chord. And it'll sound good, because there are no avoid notes in either of these. This is especially true when the lydian b7 sound is needed (see lydian b7 for more on that).

How do I become friends with the altered scale?

A tough question, I'll grant you that. It takes time to 'hear' the altered scale. It is not as easy as mastering the sound of the mixolydian scale, for example. The more you play it, the more you'll hear it. It's just a matter of practice. Try to play it in different dominant contexts, and see where you like it. Play altered licks, and practice them in all 12 keys.

A little 'trick'

There are many things you can do using the altered scale, but one of the most famous 'tricks' is this. Take a C altered scale - C, Db, Eb, E, F#, Ab, Bb. Looking for major triads, we find only two - F# major (F# A# C#) and Ab major (Ab, C, Eb). When you have a C7 chord, try playing these two triads over them. Or for any altered key - play the #11 and #5 triads. These are great for upper structure voicings on the piano, and are great for soloing.

Okay, I've said enough. Now go practice.

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