That's what they make free audio editors for.
I have a problem that's been with me ever since I started hitting puberty, which is the size of my tongue. I only have the clear diction that I do—tending toward the overprecise—because I sat down almost two decades ago with a copy of
The Oxford Book of English Verse and drilled myself all summer vacation. I'd tape record the results, and if I couldn't understand what I heard, I'd go back and read the same thing again as many times as necessary.
Anyway, when I record more than ten minutes at a time, I start to get tired and lose control a bit, slurring my words along the way. Therefore, I always give myself frequent breaks and pick it up later, editing out the pauses between.
I'm insistent on clear diction for myself because I'm a person who believes that the reader shouldn't stand in between the listener and the text. I much prefer readers who can take a piece of text and read it crisply and correctly, leaving me with the luxury of putting my own emotional response to the text.