Hello and thank you for the post and the replies.
It great to see math channels getting such use as they reveal so much more detailed contained within the original capture.
For cylinder balance the crank sensor would be the preferred choice but that's not to say we cannot use the math channel on any signal like ALT Ripple or those mentioned above.
The ALT Ripple can be notoriously unstable regardless of engine condition and for this reason I tend to steer clear unless this is all you have to work with.
Lets face it, we have to work with what we have.
In the scenario above Luca, the frequency math channel is dropping due to the crossing point of the signal falling below the threshold. (See image below)
In this scenario, if you are happy with the output of the alternator (DC coupled) then switch the scope coupling to AC. Here we reject the DC and have the Ripple presented about zero volts.
This then makes for a stable crossing point on which to create an RPM math channel to evaluate cylinder balance.
I hope this helps, take care.......Steve