Here's the first thing you need to know. Exhaust does not propagate through the pipe smoothly with a single pulse per cylinder. Constructive and destructive interference in the overall pressure wave from the individual pressure waves from each cylinder meeting the others in the pipe results in a flow that has a peak once per combustion cycle. We hear (and feel) this as pulses in the exhaust pipe. They will occur every revolution in a 2-stroke engine, and every

*other*revolution in a 4-stroke engine.

The second thing you need to know is there should be exactly two frequency curve points. One at a idle and one at maximum RPM.

The third thing you need to know is the idle and maximum RPM values for the engine you are working with.

The basic procedure for any given clip looks like this:

1.) Count the number of exhaust pulses in your clip and divide by the length of the clip, in seconds. For a two stroke engine, this is the number of revolutions per second. For a four-stroke engine, multiply by 2 to get the revolutions per second. Multiply by 60 to get the revolutions per minute of your engine clip.

2.) Divide the idle RPM value by the RPM of your clip and multiply this by the clip sample rate. This is the idle value for your frequency curve (variable2=0.0).

3.) Divide the maximum RPM by your clip RPM and multiply the result by the clip sample rate. This is the maximum RPM value (variable2=1.0).

4.) Build your frequency curve. You're done. Move on to the next clip. Rinse and repeat.