| great info, thanks! My understanding of the OEM system is as follows:
The OEM knock system does all of its filtering in analog circuitry, there is no DSP in the microcontroller. The knock sensor signal is first band-pass filtered, rectified and then integrated (averaged) over an interval of the combustion stroke. This average signal (knock level) is then passed along to the microcontroller for use by the actual knock detection algorithm.
The microcontroller maintains a background knock-sensor noise level for each cylinder (only re-calculated under non-knocking condition) which, along with the cylinder's knock level and the value from the knock-limit table for the current RPM, is used to determine if knock has occurred. So according to that document its sounds like the OEM system is doing a couple things right:
per-cylinder knock thresholds
per-cylinder non-knocking background noise levels its disadvantages vs. more modern systems are:
no per-cylinder timing adjustment
a single fundamental detection frequency (due to lack of DSP)
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