"But you blast your music all the time!"

At first glance, it's a contradiction: I say I'm very sensitive to noise, but I turn my music way up (especially if I need to concentrate or regulate). Why is that?

It comes down to the properties of the noise. Unexpected sounds like objects falling, a dog barking, or the house creaking are jarring because a) I usually can't control them, and b) the noise is not constant. What I mean by "constant" is that the pitch varies, how loud the noise is varies, and the frequency of the noise varies. I can't predict when it's going to happen or what it's going to sound like, so it's very difficult to prepare or regulate in response to it.

Compare this to, say, a favorite song. I know exactly how the song goes. I know the lyrics, the vocals, the instrumentation. I can pause and play at will. I can control if it repeats. I know exactly what to expect.

If I have to sit down and do work for a long period, it's very common for me to put a song that I know well on loop. The feeling is akin to oiling the hinges on a door. I believe I can think better and work better if all I can hear is highly predictable and enjoyable music.

Fun fact: Probably at least a third of my second YA fiction novel was written while listening to a song called "Highway 1." It was my "writing song" for a very long time.

Aside from their predictability and familiarity, why do some songs in particular seem to make it easier for me to focus?

Good question! I'd love to study this sometime in a lab via EEG or fMRI.

Some sounds also have a calming effect for me, but this phenomenon has been studied much more than my music example. I especially enjoy the sound of rain and, if possible, will open my windows to hear a rainstorm better. I also prefer 528Hz if we're speaking of frequencies associated with the various chakras. Interpret that as you will.