In music, block chords are chords or voicings(jazz) built below the melody to create a 4-part harmonized melody line.

This is a commonly technique to harmonize a melody in a jazz tune. On this basis technique there are some changes:

• block chords (generic)

• block chords double melody (commonly called "Shearing voicing").

with an additional 5th part that doubles the melody an octave down.

• drop 2 (not properly block chord)

with a voice (the second note from the top) dropped an octave below. This create an 4th part chord.

If the melody note is part of the chord, the harmony notes are also taken from the chord. This is a good technique if the melody note is diatonic (and not chromatic)and use diminished chords for the notes that are not part of the chord and it is considered a passing tone and the harmony is created by either a diminished chord (or a chromatically shifted chord). Before creating the harmonies, the chords could be converted to 6th chords, but this is not a rule. Here it's an example of harmonization of a C major scale with block chords. The first one uses three diminished chord on the D, F, and B notes. Note additional diminished chord on a G#, out of C major scale. This create a balance in harmonization of this scale, using all four existing diminished chord.

Story

The pianist George Shearing was a master in this first technique, because this is also commonly called Shering voicing. Block chord and doubled melody are used prevalent in a melody line with swing feel and to strenght the melody and to create a rhythmic background as the great orchestras of the past (Count Basie, Duke Ellington). Every pianist and arranger use this technique in a personal way. On generic block chord is used an other commonly way, called drop 2, that sound more light and fewer heavy.

Examples

Here there are some examples with the passage from melody (in F major) line to a block chords:

Chord Scales (WholeNote)