For a particular voice-over, the speaker...doesn't exactly have "slurred" speech, but they have some kind of...loose speech, it's not a distinguishable accent, they simply don't open their mouth very wide to enunciate words properly.
For instance, they might say "propa-ly" instead of "propER-ly" or "I jus want to thank you..." instead of "I jusT want to thank you...". Is there any technique for sharpening speech to get rid of that?