This taken from an EVO forum:
The ECU has logic that learns and constantly adjusts to the background noise of the engine (up to a point) and pulls timing for any amount of noise above that learned threshold. The further above the threshold, the more the adjustment will be made, such as pulling ignition timing, increasing fuel, etc.
It is a very complex process that involves many variables and inputs, one obviously being the knock sensor, but others include the RPM, the particular fuel/timing maps that are being used at that moment, etc. Also, the ECU will keep these adjustments in effect for a certain amount of time (revolutions) depending on conditions.
But, basically the stock ECU does a great job...it's just that we can't see it happening, and that's why we want devices like a Knock-Link. Because even though the ECU is doing many things to react to the knock, when you modify our cars, that may not be enough. So, we need to know exactly what our knock thresholds are to tune close to, but not beyond, them.
If you really wanted to build a 'knock meter', build something that will flash a light or something when timing is being pulled by the ECU. That will tell you that the ECU detected knock. But, in order to do that, you would need to know the timing tables of the stock ECU based on the airflow tables that you are currently on (depending on RPM, load, etc) and be able to know what the timing should be and what the actual timing is. Anytime there is a difference, that would be because of knock.
The best product by far that I know of that does this is DSMLink. I have had it for years in my Eclipse, and I am tempted to put one into my Evo. But, I sort of want to wait for a native Evo version. But, I may just do it anyway.
