Contrary to what the above posters have said, a cat is not going to have much affect on the sound/tone of your exhaust. Catalytic converters aren't designed to muffle, they're designed to (more or less) filter your exhaust. If you want a deeper tone, look into getting a bigger muffler. If you have a tiny-ass fart can it's going to be loud, high pitched, and raspy, and if you have a gigantic fart can it's going to be loud, low, and generally shitty sounding. Long story short, stay away from fart cans. Your best bet for a low, non-ricey sounding tone would be to either A. buy something along the lines of a Thermal or RS*R exhaust (with an inline muffler, not a can-style), or build your own exhaust with an inline resonator or 2 and something like a dynomax or ES Oval muffler.