Other people sound higher or lower pitched than expected

Most likely, you are having some trouble with sample rates. JackTrip requires your audio interface run at a sample rate of 48khz. In most cases, it handles this transparently. Two common things that may prevent it from doing so are:
  1. You have some other software running on your computer which is changing the sample rate after JackTrip establishes the connection
  2. Some Windows ASIO audio interface drivers fail to update the sample rate, or provide any feedback when this happens
Either you or the person you are connected with is likely experiencing one of these problems. Try closing all other software that may be using your interface, or making sure that everything is set to 48khz.
Some interfaces provide apps that you can use to adjust the sample rate.