Part of the reason people have such strong opinions about music is that, when it is heard, it is very difficult to ignore. That might be because it engages multiple regions of the brain, or it might be due to the fact that sound carries special weight in the human brain for evolutionary reasons. Euphony might signal safety while cacophony might signal danger, for example. I have blogged about this before.
We can imagine a continuum along which there are two poles, representing absolute simplicity versus total complexity. If we accept the full audible sonic spectrum, then on one side of the continuum, we have a single sound. On the other side of the continuum, we have every imaginable sound played all at once. Essentially, on one side, we have literal monotony, and on the other side, we have white noise. Between those two extremes, we have every combination of sounds the human ear can conceivably hear.
According to this idea, music is a subset of that continuum. On the simple side of the music continuum, we have a single note, either sustained indefinitely or played repeatedly; on the complex side, we have an elaborate amalgamation of notes and rhythms that is so complex that it is impossible for the mind to unravel.
With that continuum in mind, let's consider a series of assertions.
Assertion #1: Both Poles Of The Music Continuum Are Annoying
The reason those buzzing alarm clocks wake you up is because the sound they make is annoying. That sound is identical to the "simple" extreme on the music continuum. Few of us can be subjected to that noise for an extended period of time without going crazy.
Similarly, very complex examples of 20th Century atonal music, featuring many overlapping and tonally unrelated sounds, might be the closest thing we have to the "complex" extreme. Unsurprisingly, we also find that the vast majority of human beings grow irritable upon hearing that music, at least for an extended period of time. Even the members of the unannoyed minority would find it difficult to listen to, say, five such pieces played simultaneously.
Thus we see that there is a limit to the level of simplicity, and a limit to the level of complexity, human brains are capable of tolerating in music before they grow irritable.
Assertion #2: Music Gets More Pleasing Once We Move Away From The Poles
Even a repetitive piece of music like a cell phone ringtone is sufficiently repetitive to annoy most people. But it is much less annoying than a buzzing alarm clock. Therefore, as we add small increments of complexity, we eventually move along the continuum to a sufficient degree that we arrive at the lower bound of what we might call "tolerable music."
Similarly, as we strip away elements of a complex piece, we begin to arrive at a point where relationships between notes and sounds can be formed in terms of harmony and rhythm. The point at which every sound we hear makes some sort of musical sense is the upper bound of what we are calling "tolerable music."
Thus, the continuum that runs from the lower bound to the upper bound represents the full spectrum of music we are willing to tolerate.
Assertion #3: Different People Have Different Lower and Upper Bounds
Uncontroversially, it can be noted by mere observation that different people have different levels of tolerance when it comes to the upper and lower bounds. For some, 20th Century atonal music is absolutely intolerable, while for others it offers a highly stimulating listening experience. "The Song That Doesn't End" is enough to drive many people crazy; but kids really seem to like it.
Hopefully this suffices to establish that at which points people end up setting their upper and lower bounds for "tolerable music" is dependent on the individual hearing the music. Tastes vary by individual. No two people have exactly the same taste in music.
Assertion #4: The Location Of Lower And Upper Bounds Is A Function Of Cognitive Ability
If you teach a child a simple melody, that child will play that melody over and over again until he or she has driven you nuts. That child has a higher tolerance for simple, repetitive melodies than you have. In terms of our continuum, the child's lower bound is at a point closer to the "simplicity pole" than your lower bound is.
Similarly, a music novice of any age will tend to have a higher tolerance for simplicity than a veteran musician, because the novice cannot yet understand very complex music - due to a combination of lack of exposure and lack of the necessary theoretical fundamentals - while music that is more appropriate for beginners will fail to captivate the veteran, and relatively more complex pieces will give the veteran better audio stimulation and a richer experience.
The range of music compositions we find pleasing enough to listen to without getting annoyed, therefore, is a function of a person's cognitive ability to process those sounds.
Of course, musical cognition is not purely a function of age or intelligence. One cannot know everything about everything, so it is quite common to encounter brilliant physicists who prefer Bruce Springstein to Frank Zappa or Rhodes Scholars who prefer Bob Dylan to Gentle Giant. Even among musicians themselves, some very experienced ones will not put in the work required to gain an appreciation for very complicated music, while others are so accustomed to hearing complicated music that they become intolerant of anything they understand too easily.
I wrote this post this morning to explore what I believe to be one of the most important factors determining how "annoying" a person considers music to be. I am always surprised at the froth and vitriol with which people express distaste for a piece of music, and that vitriol seems to be out-of-proportion to the fact that all that is being reacted to someone else's artistic expression.
My point is that the continuum is established by the individual's actual cognition. We have a tendency to over-emphasize the role "emotion" plays in music appreciation. I don't deny that it does, but I would suggest that cognitive intolerance rules out certain sounds before a person ever has a chance to assess the merits of those sounds on an emotional level.
Once the "annoying music" has been cognitively omitted from consideration, though, each individual has many reasons to appreciate any particular piece of music. Some of those reasons are emotional, some are academic, and some are multi-faceted and difficult to explain.