...................Now I know some of you will be sniggering away over that last posting, but for us in the steam world those sounds are very important.
They actually indicate how many cylinders the engine has, and how they are set to maximise performance and pulling power. The great engineers of the past, especially those CME's (Chief Mechanical Engineers) of the big four railways would spend much time and effort on such detail.
They would consider what the engine was to be used for, and where, what steaming capacity it required, how big the boiler should be, its type, what firebox dimensions are necessary, the drafting arrangements, on what wheel arrangement the engine should be, along with the dimensions of the cylinders, how many, and what the motion would be (outside or inside), along with the stroke length of the pistons and the type of valve gear required. All this would also have to consider the overall weight of the engine, and its route availability as far as the Civil Engineer was concerned when thinking of axle loadings on the infrastructure.
The sound of an engine gives clues as to the efficiency and health of a steam engine, as much as it does with an internal combustion engine. It (the steam engine!!) is just more complicated as you are dealing with the whole, possibly in excess of 100 ton, machine where all parts add to the sum of the total, and if any are slightly incorrect or flawed, the whole machine performs badly.