Hissing noise when connecting earbuds to MacBook

Recently I bought some high quality Sennheiser earbuds, but since using them together with my MacBook I was annoyed by a constant hissing noise when playing back very quiet parts of a song. For a while I didn't bother and just accepted it as it is, but later on I played around with some tools in /Application/Utilities and found an application called Audio Midi Setup.

Luckily I was listening to some calm music while randomly fooling around with these settings and when I changed the bit rate of the Built-In Output from 2ch-16bit to 2ch-24bit all the sudden I got an impressive increase of sound output with almost no hissing noise. It's still not perfect, but definitely much better compared to what I was tortured with before. Although, increasing the bit rate all the way up to 2ch-32bit didn't cause any significant improvement to 24 bit, that's why I went with 2ch-24bit for now.


If someone can explain what the correlation between bit rate and hissing noise is, please let me know in the comments. I'm curious to know :-)