[Grammar] pairs of sentences

[essydolphinblue]

Please can you explain the differences between the following pairs of sentences and the pronunciation differences.

she read the letter which upset me.
she read the letter, which upset me.

 

[tedtmc]

Please can you explain the differences between the following pairs of sentences and the pronunciation differences.

she read the letter which upset me. - I am upset by the letter
she read the letter, which upset me. - I am upset by her reading the letter.

not a teacher