How to play different footstep sounds at different speeds

This is starting to confuse me, lol. You see, the first person template has only a run animation that’s invisible, you can only see headbobbing or an item you’re holding. So basicly this run animation is only used for playing a sound effect when I’m walking, y’know, so when I crouch or walk, you don’t see the run animation. So I’m starting to guess this is a lot more complicated than I thought, lol.