Jeff somehow made it

Sometimes (if you're talking about Jeff Favignano from YT) he edits that to sound like it's from a police speaker.  Is that what you're talking about?

Jeff has equipment in his house next to his PC, some sort of audio control box and mic or something, so he just speaks into that and it artificially adds the distortion you hear.

someone says that,but someone says that he edited in game

He edits it post recording, it isn't something that is in the actual game.

Jeff F. uses a equalizer that was connected to his microphone giving him the ability to sound like various things (radio,megaphone,transformer) he has since went to a 22 AudioBox VSL.