Full Answer
These three monitors are how the ECU tells you what it is hearing, and reading them correctly matters more on the VB than on older Subarus because the strategy behind them changed.
First, what knock actually is. Detonation is the air/fuel mixture igniting spontaneously during the compression stroke, pushing against the rising piston and spiking cylinder pressure. The ECU listens for it with a microphone bolted to the block, tuned to specific frequencies.
The important context: these events are inevitable on any modern engine running pump gas, and Subaru's detection deliberately errs toward caution. The result is a lot of false knock, where the ECU corrects for a noise that was not detonation at all. COBB describes Subaru knock detection as using a large net - it reliably catches real knock, and it catches plenty of harmless noise with it.
False knock is especially common when accelerating from a stop while letting the clutch out, during gear shifts and particularly if you grunt the shift, accelerating at low rpm in a high gear, cruising on the freeway, and during abrupt throttle changes. If your corrections cluster in those situations, that is the pattern of a car hearing noise rather than a car in trouble.
**Dynamic Advance Multiplier (DAM)** is a global adjustment to ignition timing, expressed on the VB as a decimal from 0 to 1 with 1 being ideal.
Here is where the VB differs from what most older forum advice assumes. On direct-injection Subarus - which includes the FA24 - COBB deliberately made the DAM strategy more reactive, because premium fuel is not required on these cars. Corrections that would have shown up as Fine Knock Learning on an older non-DIT Subaru can now show up as a DAM drop instead.
So on a VB, a DAM drop is not automatically the alarm bell it is on an older car, and it is not surprising to see one, particularly on lower octane fuel. Two further points COBB makes explicitly: how long DAM takes to climb back to 1 tells you nothing about how serious the event was and does not mean the car is still knocking, and advancing DAM back up requires driving in specific load and rpm ranges without knock - so it can sit low simply because you have not driven through the conditions needed to relearn.
DAM also resets after an ECU reset or a reflash, so a low value right after flashing a map is expected.
**Feedback Knock Correction (FBKC)** is the real-time reaction. On a perceived noise the ECU immediately pulls timing by the amount shown, then adds it back toward 0 once no further noise is detected. It is momentary by design.
**Fine Knock Learning (FKL)** is the remembered correction, built from historical noise and applied to specific load and rpm ranges. Once learned into a range, it applies whenever the engine operates there. FKL values reset when DAM changes, and are re-evaluated intermittently once DAM has stabilised.
What counts as normal. COBB considers Feedback Knock Correction of roughly -2.5 degrees or less to be normal and not a major concern. The combination that warrants investigation is DAM below ideal together with corrections beyond -2.5 - and that combination is especially concerning if it happens at full boost and wide open throttle rather than at cruise or light load.
That pairing is the key. On a DIT car neither number alone tells you much. Diagnosing whether you have a real problem means looking at how far DAM dropped and what FBKC and FKL look like overall, in what conditions, rather than reacting to any single reading.
If you do have real knock, the most common cause is fuel. Use top tier fuel so your effective octane matches the rating, and if you are on an off-the-shelf map, switch down to one written for lower octane. Common mechanical causes worth inspecting are a worn MAF sensor or front oxygen sensor, boost and intake tract leaks, and excessive blow-by. Also confirm your hardware actually matches the map notes for the map you are running, and that boost is within the range those notes specify - overboosting makes knock more likely.
The practical summary: watch patterns, not single numbers. Isolated corrections in the classic false-knock situations are noise. DAM that drops and stays down while FBKC and FKL show meaningful corrections under boost is a conversation to have with your tuner.