Raul, in one word it's "bigger"; the signal is bigger on playback because the 2 track tape heads are bigger, that translates to "apparent" larger speakers, and more powerful and more forceful power amp.
The music has not been altered in any way shape form or fashion; it's just bigger, which means you can hear more detail.
The size of the heads make for a larger more forceful signal on playback.
https://www.google.com/search?q=size+of+tape+recording+heads&tbm=isch&tbo=u&source=univ&...
In addition, my deck has all "Black Gate" electrolytic capacitors, plus new original transistors. No, that doesn't make it better, but enables precise duplication of the original signal.
Maybe, the link I provided will convey what I'm talking about.