Fast weapons have an animation time of 20 frames
Everything else is 30 frames
There is a global recovery time multiplier of 1.2
default attack speed for 1H fast weapon is 20 frame animation, 36 frame recovery (50% slower due to 1H style or using a shield)
default attack speed for 1H average weapon or 2H weapon is 30 frame animation, 54 frame recovery (50% slower due to 1H style, 2H style or using a shield)
default attack speed for 2W fast weapons is 20 frame animation + 24 frame recovery + 20 frame animation + 24 frame recovery default attack speed for 2W average weapons is 30 frame animation + 36 frame recovery + 30 frame animation + 36 frame recovery
Dexterity affects both animation speed and recovery time Everything else only affects recovery time
If you record a 30 FPS video of yourself making an attack unarmored and do a frame by frame - you'll be able to reproduce these exact times.
I can't quote the source because it's from the paywalled Something Awful forums (Josh Sawyer, lead designer).