It’s a combination of RIAA equalization, mastering suited to vinyl, some distortion, and some surface noise (mostly unobtrusive clicks and pops), according what my ears report me while listening to vinyl.
I'm listening to the same Hi-Fi system since I'm six. I have both vinyl and CD versions of some albums (I only buy vinyls of albums which I like a lot, and listen it with a coffee or tea), and they really sound different.
I don't think it's because it's feeding the nostalgia, because I can feel the same things regardless of the medium and system I listen to these albums/songs.
I don't think soothing the brain angle is valid either. I get the same enjoyment and relaxation from both mediums.
For me, CD brings the enjoyment of a well brewed coffee, but vinyl brings the same feeling when you (sometime accidentally) brew that elusive perfect coffee for you. It needs some time and intention to appreciate.
I'm an ex-orchestra player though, so my experience may not reflect the views of bigger audiophile crowd.
