An increase in subglottal pressure most likely affects which vocal characteristic?

An increase in subglottal pressure directly influences vocal intensity. Subglottal pressure is the air pressure that builds up beneath the vocal folds in the trachea. When this pressure increases, it enables the vocal folds to vibrate with more force and amplitude, which results in a louder sound output. Therefore, the intensity of the voice is directly correlated to the amount of subglottal pressure present.

In contrast, while vocal resonance, fold adduction, and pitch can also be affected by various aspects of vocal production, they are not as directly linked to changes in subglottal pressure as vocal intensity is. Vocal resonance pertains to the amplification and tonal quality of the voice shaped by the vocal tract's configuration. Vocal fold adduction refers to how tightly the vocal folds come together during phonation, and vocal pitch is influenced more by the tension and length of the vocal folds rather than subglottal pressure alone. Hence, the clear connection between subglottal pressure and vocal intensity underscores why this is the correct answer.