To rule out a tach hardware issue (e.g, with the sensor board, flywheel striping) mark a driver wheel with a "dot". In the default 4 chuffs/rev setting count the EXACT number of wheel revolutions to get some EXACT number of chuffs. In other words, saying 1-3 is not good enough! This only takes a minute or two so do it a couple times at slow speed so that you can see the "dot" pass top-dead-center (or whatever angle). This should be a repeatable number...1.3 chuffs/rev, 1.9 chuffs/rev, whatever.
THEN, change via DCS to 7 or 8 chuffs per rev which apparently gets you close to 4/rev. Again, at slow speeds count the EXACT number of wheel revolution to get some EXACT number of chuffs.
Is the ratio EXACTLY 8:4 or 7:4? This will tell you if there is an incorrect parameter in the sound file.
