It is partly due to the internal design of the engine. The cylinder firing order has an effect. A lot of the sound is down to the design of the exhaust system.

Vehicle manufacturers will tune the exhaust system to get the sound they want. The sound from the exhaust system is affected by the length of the pipes and the amount and design of the silencers (mufflers).

American muscle cars don't rev as highly as European supercars which also has an effect on the sound. Lower revs results in a lower pitched sound.