The exhaust note is the resonant tone produced by an automobile exhaust. It is affected by, among other things, the size of the pistons and the shape of their surface, the shape of the combustion chamber (the cylinder), the shape and position of the exhaust valve ports, the shape, size, and design of the exhaust manifold or header, the design (and/or existence) of the catalytic converter, the length, diameter, and the bends in the exhaust pipe, and the characteristics of the muffler, if it is present.