Analyze the use of reharmonization in a given jazz standard, identifying specific alterations and substitutions and explaining their impact on the overall sound.

Reharmonization, a crucial technique in jazz arranging and improvisation, involves altering the original harmonic structure of a melody by substituting or modifying chords. This practice allows musicians to reinterpret familiar tunes, adding new layers of complexity, color, and emotional depth. Reharmonization can involve various alterations, such as chord substitutions, chromatic alterations, modal interchanges, and the use of different chord voicings. The impact of reharmonization is significant, fundamentally changing the harmonic context of a piece and influencing its overall sound.

One of the primary forms of reharmonization is chord substitution. This technique involves replacing a chord with another that shares a similar harmonic function or quality. A common example is the use of tritone substitutions, where a dominant 7th chord (V7) is replaced with a dominant 7th chord a tritone away. For example, in a ii-V-I progression in C major (Dm7-G7-Cmaj7), the G7 could be substituted with Db7. This substitution maintains the dominant function but adds a chromatic color, creating a slightly more complex sound. This technique is incredibly common in jazz standards, and the effect of this tritone substitution provides a new sound to a common chord progression. Another type of substitution involves using minor chords instead of major chords or vice-versa. For instance, in the same C major ii-V-I example, the Dm7 can be changed into a D half diminished chord. This adds color and creates an altered sound. Reharmonization through substitution allows the musician to alter the familiar chords, while still preserving the fundamental harmonic intent of the original chord progression.

Another form of reharmonization involves the use of modal interchange, also known as borrowed chords. This is where chords are borrowed from parallel modes or scales to add new colors and flavors. For example, in a C major context, a chord borrowed from C minor might be used, such as a flat VI chord (Ab major), which is not within the C major scale. This technique adds a sense of harmonic richness and surprise by introducing chords from different keys within the same context. This is done to create contrast in a harmonic progression. The use of modal mixture is very common, and the result is very common among jazz standards.

Chromatic alterations are another way to reharmonize a chord progression. This involves adding or altering notes to the chords to create a more complex and colorful sound. For instance, a dominant 7th chord can be altered by adding a b9, #9, b5, or #5. These alterations create tension and dissonance, making the resolution to the following chord more dramatic. For example, the standard G7 chord can be changed to a G7alt (G7b9#9) in a ii-V-I progression, adding a unique color and making it more complex. Chromatic alterations can transform the character of a chord while still retaining its primary function.

Reharmonization can also involve simply changing the voicing of the chords. While the underlying chords might not be changed, the way they are voiced changes the harmonic color and texture. Using inversions, open voicings, or close voicings changes how the chords interact and how they blend together. For example, a C major chord can be voiced as C-E-G or E-G-C or G-C-E. The voicing makes a big difference in how that same chord would feel and sound. Another example would be changing from root position voicings to a voicing where the bass note becomes the 7th of the chord. The use of chord voicings is another very effective way to reharmonize.

Now, let's consider the use of reharmonization in a well-known jazz standard like "Autumn Leaves."

In the original harmonic structure of "Autumn Leaves," in G major (or E minor), the A section often includes the following chord progression: Am7 - D7 - GMaj7 - Cmaj7 - F#m7b5 - B7 - Em7. A common reharmonization technique in "Autumn Leaves" involves substituting the dominant chord, D7, with a tritone substitution like Ab7. The result is a move from Am7 to Ab7, creating a more complex and modern sound. It also leads to a more chromatic movement. Also, the Cmaj7 in the progression can be substituted with an A7, which is the V7 chord of Dm. By doing so, the Cmaj7 would then become an altered chord that resolves to Dm, instead of the common C major chord, which brings a new color and feeling to the progression. Another common substitution is the F#m7b5, which could be substituted with D7, which creates a ii-V-I to G. This use of reharmonization gives the musician more control over how the harmonic structure sounds.

Another example of reharmonization in "Autumn Leaves" is the use of modal interchange or borrowed chords. The Cmaj7 in the progression could be substituted with a Cmin7 chord (borrowed from the parallel minor scale). The result is a shift from a bright major sound to a more melancholic minor sound. Also, the Em7 at the end of the phrase might be substituted with an E major chord, which is the dominant of A minor, the relative minor scale. This can then be followed by an A7 altered chord, creating a V7alt-i sound. This adds a dramatic effect, which also makes it more modern and interesting. These borrowed chords bring new flavors and sounds to the standard progression.

Reharmonization can also be done with chord extensions and alterations. For example, the standard D7 chord can be reharmonized as a D7alt chord (D7b9), using extensions and alterations, adding extra harmonic color to the chord. This approach also creates a more dissonant sound that still resolves in the traditional fashion of a dominant chord. The result is more dramatic tension and a more pronounced resolution.

The impact of these reharmonizations is significant. The use of tritone substitution adds a chromatic feel and unexpected twists to familiar progressions. Modal interchanges create a wider range of colors, and chord extensions and alterations create added complexity and tension. Changing the voicings also adds a new dimension to the harmonies. The overall impact of reharmonization is that the original song will sound new, modern and with more complexity and depth. The use of reharmonization is what gives many standards their specific and unique sound. It is a vital tool for creating unique and interesting harmonic landscapes within the standard song format.

In conclusion, reharmonization is a powerful technique for jazz musicians to explore familiar chord progressions. By applying alterations, substitutions, borrowed chords, extensions, and different voicings, the musician can explore new colors and complex harmonic landscapes. This makes the music more expressive and unique, and provides the listener with a more exciting and engaging experience.