Cats have 10 times as many vocal chords as dogs. Dogs have 10 and cats have 100.
Cats can vibrate the muscles underneath their vocal folds, very slowly, producing a purr. Domestic cats purr at a rate of about 26 cycles per second, similar to the frequency of a diesel engine as it idles. Purring doesn't always mean the cat is happy. It can also be a sign that a cat is in pain or some distress.
Cats rarely meow at each other, reserving this sound for their interactions with humans.