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سه‌شنبه 23 خرداد‌ماه سال 1391 ساعت 02:24 ق.ظ

Blues

مطلب زیر توسط آقای میلاد فرزین فر از شاگرداهای استاد جمع آوری شده و در مورد بلوز می باشد.



Blues Chord Progressions and Variations

The blues chord progression, or 12 bar blues progression, is a standard I-IV-V chord progression that spans twelve measures. While there are a few extremely common twelve bar progressions that repeatedly pop up, there are even more variations on the standard formula. Take a look at my earlier post about the 12 Bar Blues Progression for the basic outline and general information, because in this post, we’ll be looking at some of the common variations.

Standard Variations

These first two blues progressions are basic in their construction, only changing a few chords, primarily the durations of the V chords and placements of the IV chord.

This first progression is the most basic, but notice how I notate each of the changes. The changes are relative to each other.

For example, if one were to play in the key of E:

The I chord would be an E

The IV chord would be an A

The V chord would be a B

If one were to play in the key of C:

The I chord would be an C

The IV chord would be an F

The V chord would be a G

The keys of E and A are more popular with guitarists than with pianists, who prefer C or G, because of the tuning of the guitar and the number of accidentals on piano. Let’s look at a common modification to blues chord progressions.

Common Blues

Notice the addition of the IV chord in the second bar, this serves to break up the beginning of the blues progression. Without it, the progression can become stale while sitting on the I chord. This is the most common chordal variation on the blues progression.

Also notice the addition of the IV chord in the 10th measure, this serves to create more movement, leading to the return of the I or root chord. This is another very common variation.

And last is the addition of the V in the last measure, this serves as the “turnaround,” a common blues device that states the end of a progression.

Jazz Variations

The use of blues chord progressions is extremely common in jazz, especially in the big band or bebop genres. Below are some examples of typical variations, however, this time I’ve included the changes in the key of F for simplicities’ sake.

Big Band Blues (Basie Blues)

Notice the similar construction in the first four bars, the only changes are the addition of the diminished chord and the minor 7th chord which serve to create movement and color.

Again, in the 5th bar, we see the diminished chord following the IV chord. The basic idea behind the placement of the diminished chord is that the harmony remains relatively stable while the bass note raises a half step to create tension.

In the 8th bar, we see the chord change to a VI chord, a change uncommon in basic blues. This serves to create color and movement leading into the cadence (or last four measures).

In the 10th bar we see a distinct departure from the standard blues cadence, the IIm7 chord creates some tension and is an inversion of a V9th chord.  Again, we see implied chordal harmonies adjusting with changes to the bass note.

Bebop Blues

Notice the similarities in the bebop blues and big band blues? While they are very similar, bebop blues are designed to be played extremely fast. At these high speeds, the chordal harmonies often act as the melody. Each chord change leads nicely to the next.

The first four bars are identical, but the bebop blues is without the diminished chord.

The second four bars are very similar, but the bebop blues adds a IIIm7 chord before the VI7 chord, again, to create movement leading to the cadence.

The first two bars of the cadence are identical to the big band changes but the turnaround (final two bars) are not. They lead down in perfect major fourths to the root, A-D-G-C and finally back to F. This creates movement that anticipates the I chord.

 

Blues scale

The term blues scale is used to describe a few scales with differing numbers of pitches and related characteristics. See: blues.

The hexatonic, or six note, blues scale consists of the minor pentatonic scale plus the 4th or 5th degree. A major feature of the blues scale is the use of blue notes, however, since blue notes are considered alternative inflections, a blues scale may be considered to not fit the traditional definition of a scale. At its most basic, a single version of this "blues scale" is commonly used over all changes (or chords) in a twelve bar blues progression. Likewise, in contemporary jazz theory, its use is commonly based upon the key rather than the individual chord.

 

The heptatonic, or seven note, conception of the "blues scale" is as a diatonic scale (a major scale) with lowered third, fifth, and seventh degrees and blues practice is derived from the "conjunction of 'African scales' and the diatonic western scales". Steven Smith argues that, "to assign blue notes to a 'blues scale' is a momentous mistake, then, after all, unless we alter the meaning of 'scale'. Indeed, the A minor pentatonic scale does have many uses.Many blues songs have just three chords, the I, IV and V chords. In the key of A, that's A, D and E

source:From Wikipedia, the free encyclopedia