Why do all the muscle cars sound different before the Clean Air Act mandated catalytic converters?

AFAIK original equipment cars did not have to add on a CAT.  Just that there is no old cars left. Engines wear out, and cars rust or get smashed. 

The cat is like a muffler but different.  It is a pre muffler that is welded into the exhaust pipe after the exhaust manifold.  It is filled with stuff to extract out carbon monoxide gases from the exhaust by a chemical reaction. The exhaust has to go through this first (which kills some of the sound and then through a muffler which muffles out more of the sound.  Quiet is the new "Cool"

It's not the converter. It's the motors with less horsepower and emission restrictions that ruined muscle cars. 

The exhaust gas goes to another restriction.  The sound will be different.

The point of a muffler is that there is no direct route from the engine to the outside air.  As exhaust is detoured through the muffler, it loses a lot of the sound pressure.  The purpose of a catalytic converter is different, but it also detours the exhaust, causing a drop in sound pressure.  

So essentially, if a car has a catalytic converter and a muffler...then it has two mufflers.  Or two components that act like mufflers.

more to performance than how it sounds every tosser that has banged on about how good their car sounds has lost the drag race wanna go for pink slips?

My wifes I30 sports kills my '71 350 chev powered Monaro in a drag race, makes more top speed and has more brakes.

The ole chev makes the noise when the 4 barrel opens but it hasn't got the goods.

 It sounds better than the ls3 powered commodore. But if you wanna go fast the ole chev is yesterdays technology.

The converters are full of pellets that remove the pollutants. These pellets are very restrictive and slow the flow of exhaust gasses. It's like blowing through your fist, it sounds different.