Varying dynamics is another ‘secondary variable’ of strumming. Much like string selection, it can be a great tool of expression when strumming, yet an awareness of it is not necessarily required to strum effectively. Again, just like string selection, use of dynamics often occurs naturally to the guitarist and its subtleties vary in a similar, unpredictably expressive fashion.
Dynamics, in a nut shell refers to the volume of the strumming. Loud and soft and everything in between. While dynamic variation occurs in every strumming pattern that you ever hear (intentionally or otherwise) it is almost never annotated. Doing so would be an almost ridiculous task. Accents can often be used to emphasize a certain strum, or beat of the bar, but it is almost impossible to go through every strum of a song and accurately describe its velocity or volume. So why write about it here? Because although it doesn’t always get a mention on the sheet music, it is a very prominent and important characteristic of strumming and it is important to experiment with dynamics, or at the very least be aware of its presence when learning to strum. Think of it like altering the pitch of the voice in speech. You don’t necessarily think about how you are modulating pitch, but to not change pitch would result in a very weird, robot like voice. As well as that, altering the pitch in an unusual or forced way sounds strange and uncomfortable.