The Instability of Certain Scales in Music: A Musical Exploration

Renowned for their complex and unique properties, certain musical scales are considered unstable. In this article, we delve into why the scales such as the Locrian, Melodic Minor 7, and Altered Scale are labeled as unstable, focusing on the inharmonious sound patterns and the physics behind their dissonance. Although the term ‘unstable’ may not be commonly used in musical discourse, the reasons for these scales' dissonant nature are rooted in the relationship of their frequency ratios and overtones.

Understanding Musical Scales and Their Frequencies

Music scales are formed by a series of notes, typically starting from a root note. These notes create harmonics that either fit together pleasantly (consonance) or clash (dissonance). The stability or instability of a scale is often determined by these harmonics, particularly the intervals between root notes and their related overtones.

The Case of the Locrian Scale

The clarity of this explanation can be seen through the example of the Locrian scale, which is highly unstable due to its inherent dissonance. The Locrian scale is built upon the seventh degree of a natural minor scale, starting on the note that is usually considered the seventh. I will demonstrate how the intervals derived from the Locrian scale create a sound that can be perceived as unstable due to their dissonant nature.

Interval Analysis: Major Thirds, Minor Thirds, and Tritones

The primary triad built on the root of the Locrian scale is a minor triad, with intervals such as a minor third (4:5) and a tritone (18:25). Let’s analyze these intervals in more detail:

Minor Third (4:5): While a minor third is not entirely dissonant, it can still create a sound that is not entirely consonant, especially when used in certain musical contexts. Trimate (18:25): Often referred to as a tritone, this interval is considered the most dissonant in Western music. It arises from the lack of consonant relationships between its harmonics. To understand why, consider the following:

The frequency ratio of 18:25 is in stark contrast to the more pleasant consonance ratios such as 1:2 (octave) and 2:3 (perfect fifth). These consonant ratios are simple and align with natural harmonic series, where overtones are related. For example, in an octave, the higher harmonic is exactly double the frequency of the lower, and the perfect fifth is three-quarters or three-fifths of the frequency of the lower note. Conversely, the tritone, with its frequency ratio of 18:25, does not fit neatly into this pattern, leading to a unique dissonant sound.

Visualizing Dissonance: Frequency Ratios and Overtone Series

To further understand the instability of the Locrian scale, let's visualize the overtones associated with the root and its fifth in the C Locrian mode. The overtones of a note provide a window into its harmonic structure:

First Example: Overtones of Root Note (C Locrian) - 18:25 Last Example: Overtones of Fifth Note (G Locrian) - 18:25

The overtones of the root note (C Locrian) and the fifth note (G Locrian) are completely unrelated. Comparing the frequency ratios, C to F (18:25) and G to C (18:25) illustrate how the lack of harmonious relationships between the notes contributes to the instability of the scale.

Alternative Scales: Melodic Minor 7 and Altered Scale

Other dissonant scales share similar properties. The Melodic Minor 7 scale features a tritone and can sound unstable similarly to the Locrian scale. Additionally, the Altered Scale, which is a variant of the Melodic Minor 7 with a double flat 7, also exhibits significant dissonance.

Expert Perspective and Conclusion

A master’s in music, coupled with extensive study of Asian traditions, provides a unique perspective. While the term ‘unstable’ may not be commonly discussed in the realm of musical scales, it accurately reflects the experience of listening to these scales. The instability arises from the complex and inharmonious relationships between the notes and their overtones, contributing to the overall dissonant nature observed in these scales.

This exploration of dissonance in music offers a deeper understanding of why certain scales are considered unstable and sheds light on the complex harmonics that underpin the fundamental nature of musical sound. Whether used for expression or for experimentation, these scales offer a fascinating glimpse into the intricate world of dissonance in music.