Describe how a composer might use quartal harmony to create a unique and modern sound within a jazz context.

Quartal harmony, which is based on intervals of fourths instead of the more traditional thirds, offers a unique and modern sound within a jazz context. Unlike tertian harmony, which is derived from stacks of thirds (as in the traditional major and minor chords), quartal harmony uses stacks of fourths, creating a more open, ambiguous, and often dissonant sound. The use of quartal harmony allows composers to move away from the familiar and predictable sounds of traditional jazz harmony. It offers a way to create fresh sonic landscapes and expand harmonic possibilities.

One of the key ways composers utilize quartal harmony is by creating chords built from stacked fourths. For example, instead of a typical C major chord (C-E-G), a quartal voicing might be C-F-Bb. This simple example demonstrates how different quartal harmony sounds compared to tertian. Using these voicings can create chords that lack a clear sense of major or minor, creating a more ambiguous harmonic environment. These open-sounding voicings often feel less resolved than traditional chords and have a more modern and spacious feel. The use of quartal voicings also provides more flexibility in how chords are voiced, allowing composers to create interesting sounds.

Another approach is the use of quartal harmony in melodic lines. Composers can create melodies using fourth intervals to give a unique contour and feel. This contrasts with traditional jazz melodies that often rely on scale-based patterns and arpeggios. Quartal melodies are often more angular and unpredictable, and lack a sense of a traditional melodic structure. The use of this gives an unconventional and distinctive feel, setting it apart from melodies based on tertian harmonies. The combination of quartal melodic lines and quartal voicings can create a strong sense of unity, giving the music a very specific harmonic fingerprint.

Quartal harmony can also be used in combination with traditional tertian harmony. A composer can use a mixture of traditional harmonies and quartal harmonies to create a contrast, and to add depth to a piece of music. The juxtaposition of familiar and unfamiliar sounds can also add to the effect. This contrast can add a layer of complexity to a composition and makes it sound modern. This integration allows composers to use the unique sounds of quartal harmony in a way that’s not so jarring that it makes the harmony too dense. It’s a balanced method of using quartal harmony within the context of traditional harmony.

Quartal harmony can also be applied to dominant chords to create a more modern or altered dominant sound. For instance, a dominant 7th chord can be altered using fourths to give a more angular and dissonant sound. For example, the G7 chord might be voiced as G-C-F instead of G-B-D-F. This altered dominant chord maintains the dominant function (because of the tritone between G and F), but the use of fourths changes the sound dramatically. This is a way to add a modern sound to a familiar jazz chord progression, and gives improvisers new harmonic options to explore, while retaining the general harmonic structure of the song. This is a great way to add a modern twist to a traditional chord progression.

Here are some specific examples of how a composer might use quartal harmony:

1. A chord progression using only quartal chords: Instead of a ii-V-I in C (Dm7-G7-Cmaj7), the progression could be built using quartal voicings. The Dm7 becomes D-G-C; the G7 might become G-C-F; and the Cmaj7 might become C-F-B. This creates a harmonic environment that lacks a strong sense of tonality and adds a very modern and unusual flavor to the music. The overall sound is more open and less resolved compared to the standard chord progression.

2. A melody line based on fourths: A melody could start with a C, then move up a perfect fourth to F, then up another perfect fourth to Bb. This melodic line has an angular and disjunct quality compared to traditional melodies. The overall feel is less traditional and more dissonant. It's a unique way to write a melodic phrase. This approach forces the improviser to explore unconventional melodic ideas, expanding their palette.

3. Combining quartal harmony with tertian harmony: A song might have a traditional A section with tertian harmony, and then go to a B section that utilizes quartal harmony to provide a very clear contrast. This contrast helps to add harmonic diversity to the song. The juxtaposition of these two methods creates an interesting and engaging harmonic texture.

4. Quartal voicings on dominant chords: To create a different sound on a dominant chord, one could use a voicing based on fourths. A typical G7 would be G-B-D-F, but with quartal harmony, it could become G-C-F. This gives a dominant chord a more open and dissonant sound. It also alters the sound without altering the primary function of the dominant chord.

In summary, quartal harmony provides composers with a valuable tool for creating a unique and modern sound within a jazz context. Its use in both chord voicings and melodies opens up new harmonic territories, allowing for more complex and unpredictable musical experiences. The combination of quartal harmony with traditional tertian harmony allows for an effective and nuanced way to create rich, and modern soundscapes. This approach pushes the boundaries of traditional jazz harmony while still remaining within the genre's broader scope.