monotonous

This term describes a specific kind of boredom rooted in repetition and a lack of change. While "boring" is a general term for lack of interest, "monotonous" specifically evokes the image of a flat line or a repeating loop, suggesting that the lack of variety is the primary cause of the tedium.

When applied to sound, it refers to a literal lack of melodic or tonal variation. This creates a psychological effect of drowsiness or mental fatigue, often associated with mechanical processes or uninspired speech.