Generally speaking, when you receive downvotes it is good to reference the site voting guidelines. Not everyone can downvote on questions, but users with a reputation of at least 125 points can downvote whenever and for whatever reason they choose. That does not mean that all downvotes are equally valid, and the voting privilege can be abused; in particular, serial upvoting and downvoting, and other types of voting fraud can lead to suspension for offenders.
If you hover your mouse pointer above the downvote arrow on a question, you will see: "This question does not show any research effort; it is unclear or is not useful." If you hover above the downvote arrow on an answer, you will see: "This answer is not useful." This seems to indicate that the utility of a question or answer is one of the significant factors in evaluating a question or answer. The goal of Stack Exchange is to provide a searchable repository of high-quality questions and answers, so it would seem that this utility must extend beyond the asker, to future guests of the site.
You could also visit the Why is voting important? help page, where you will find:
Voting up a question or answer signals to the rest of the community
that a post is interesting, well-researched, and useful, while voting
down a post signals the opposite: that the post contains wrong
information, is poorly researched, or fails to communicate
If you have made a genuine effort to understand why you have received a downvote, but still can't make any sense of it, the best course is probably to just forget about it. Votes are meant to indicate quality to future visitors, but this is an imperfect system. Sometimes votes are just inexplicable. This kind of thing will average out over time; if you see a lot of downvotes on your posts, then there might be a problem and you should probably reassess your posts.
In the absence of any comment, you don't know if the downvoter was having a bad day, has an axe to grind about some particular topic, or has some thoughtful reason to take issue with your post. It is nice to have comments to accompany a downvote, but it is not required (and voting is anonymous). I actually think that this is a good thing. Sometimes I leave a comment with a downvote, sometimes I don't. I think that I am more likely to vote to close a question than I am to downvote it, and I may or may not leave a comment when I vote to close. There have been a few cases for me when I left a comment, even without a downvote, that was critical of a question and suggesting improvement, only to be met with hostility and personal insults. Certainly most users of the site behave better, but it doesn't take too much of this sort of thing to make you think twice before leaving critical comments.
In your particular case, I only see one question with one downvote. This question is about "how to correctly label suspension chords using chord symbols." It is a little unclear to me exactly what you are looking for here, and if the posted answers are an indication of what you were seeking, this is pretty basic stuff. That does not mean that your question is out-of-bounds for the site, but someone (and I did not downvote this, I am only speculating) may have thought that your question was either a little too unclear, or that it did not show any research effort.
If you participate on SE Music, you will get some downvotes. It looks like you have one downvote in eight question posts; that is not a bad ratio, so don't let that worry you. When they do come, just take downvotes as critical feedback and try to keep improving your posts.