A polychord consists of two or more chords played together and such chords may be originated from the same or different tonalities – usually the latter is applied. Generally, the used chord in the polychord structures must be perceived independently, although it is not mandatory. Nevertheless, when the chord pitches are mixed, the overall chord structure will be considered as one complex unit:
If you wish to represent polychord structures they are usually separated by a vertical bar. For instance, if you have the C and Ab major chords played as a polychord, they would be written as C|Ab. In this particular case, polytonality or bitonality is implied since we have chords from different tonalities, as in the example above with Em and Eb. Normally, as with clusters, if you want the individual chord formations to be heard distinctly, they should be properly spaced since depending on the way that the involved chord notes are arranged, more or less tension can be created.
When polychords are built from chords in the same tonality, they can be considered, in fact, as chord extensions. As an example, if you have a C and a G major chord from C major tonality, you can either represent it as a C|G or Cmaj9.
As for the resonance of polychords, it is advisable to follow the logic of how the overtones are produced – from wider to closer interval relationship. So, in order to achieve a better overall resonance, one chord would be in open position voicing at the bottom and the other chord with close position voicing at the top:
As mentioned, the perceived quality of the dissonance and consonance of polychords, as with any other chord formation, has to do with where dissonant or consonant intervals are placed. The use of consonant or dissonant intervals in the outer voices of a chord structure tend to have a deeper impact in the way we perceive a chord as a whole:
The ability to regulate the tensions should be exercised by you according to the desired effect. As with clusters, some of the consonant or dissonant quality may be enhanced or dispelled according to how closely you place both chords; by the way you voice the chord structure and its register; by the way that the involved chord notes are presented; or by arpeggiating one or both chords:
Polychord structure and voicing is maintained but it is presented in three different ways
Any type of chord can be used to build a polychord but three note chords are usually more common. However, the decision of the chord quality and their extensions are entirely up to the composer and the harmonic and melodic impetus.
Until now, we have been looking at polychords with two triadic units, but more chords may be used in the construction of a polychord:
Again, the way you use polychord structures will depend on the effect and sensibility you are going after. In terms of tonality and harmonic implications, the more chords are involved, the more complex and ambiguous the musical passage.
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