[TR] [6pack] Compression boost

[Randall]

> I seem to recall reading that knock sensors are far from 
> trivial and that much signal processing and FFT's are 
> required for effective implementation.  If so, transplanting 
> a knock sensor tuned for one engine onto a drastically 
> different engine (inline six vs V6, solid lifter vs 
> hydraulic, etc) is unlikely to be fully successful.

I've read much the same thing.  Article I saw talked about the "knock
signature" being different for every engine.  Apparently they don't do the
tuning in the sensor (which is basically just a microphone) but in the
attached computer/DSP.  The more advanced ones also use a sliding window
algorithm that tracks the crank angles where knock is likely to occur, and
compares sound within the window to sound outside the window; in certain
frequency band(s).

Here's a chip that implements the simpler version :
http://focus.ti.com/lit/ds/symlink/tpic8101.pdf

Randall