In music, what does 'crescendo' specifically signify?

The term 'crescendo' is a musical directive that specifically indicates a gradual increase in loudness over a passage of music. This dynamic alteration allows composers to create an emotional buildup, intensifying the musical experience for the listener. By marking a section with a crescendo, the performer understands to gradually play louder until reaching a peak or a specified volume.

In contrast, the other options reference different musical expressions. 'Decreasing tempo' refers to a slowing down of the pace of the music, which is not related to dynamics. 'Emphatic playing' signifies a style focused on strong accents and expression, rather than a gradual change in volume. Lastly, 'soft dynamics' denotes a quiet playing style, which is the opposite of what a crescendo represents. Understanding these distinctions enhances the interpretation and performance of musical works.