How are effects applied to audio files? What changes are made to the binary/hex representation of the file?

I have been looking into how effects are applied to audio files by software such as logic, pro tools, etc. Im mainly concerned with MPEG-1 (.mp3) files at the moment, however if there are easier files to play around with I am open to new ideas.

What is happening to the audio file that distorts the sound, changes the pitch, slows it down, speeds it up?

I understand that .mp3 files are organized into frames, and that the frame header contains information about the data that follows it. However, I am having trouble finding a reliable way to identify a frame in the hex representation of an .mp3 file.

I would really appreciate any information/links to information that anyone has on this topic.

Thanks!