Knock Sensor

Hi, so the frequency of knock is specific, but how does it variate in Voltage depending on the engine, Are there different knock sensors for different ranges of frequency? Modern ECU´s use a digital signal processor to focus on the specific frequency that they know knock will occur at, but how does it work, also use a piezoelectric sensor but it has a bigger ratio of noise? Any help is appreciated.

There are resonant knock sensors that provide a higher peak-to-peak voltage output at a specific resonant frequency. So a OEM might choose that work work with a specific engine and ECU.

More modern designs use a broad-band knock sensor that does not filter out any frequencies, and as you've rightly said, the DSP (digital signal processing) in the ECU digitally filters the signal to identify specific frequencies where the amplitude of the signal will represent knock.

I don't think you really need to know how the DSP works to use it with modern ECUs, and setup and tune the knock control systems. But maybe this will help you explore that rabbit hole...

https://en.wikipedia.org/wiki/Digital_signal_processing

https://en.wikipedia.org/wiki/Analog_signal_processing

https://en.wikipedia.org/wiki/Frequency_domain