Combustion noise

Combustion analyser noise description:


CA noise is a special calculation which can judge the noise resulting from the engine, based on the measurement of the cylinder pressure. The example above shows the typical modern cylinder pressure curve. The CA noise gives the approximate value of what kind of noise this engine will produce. 


When you press the Setup button on activated new CA NOISE line, the CA NOISE setup window will open:


The CA NOISE supports multiple input channels.

For detailed information about basic settings of the input and output channels see -> Setup screen and basic operation.

CA noise is calculated with a special so-called U weighting filter. This is basically a band pass filter of the cylinder pressure. Additionally, we can use the A filter (human hearing filter) to determine the human perception to the noise made by the engine.

The scaling of the input pressure must be either in ‘Pa’ or ‘bar’ in order that the math works correctly afterward, otherwise error message appear on CA NOISE line in Value column:

Math_MachDiagn_CA_nepravilne enote


There are three types of output channels available:

  • Weighted raw - the output is the time curve with applied U (and optionally A) weighting; this channel might be used in the Sound Level mathematics for advanced sound analysis.
  • Overall value - this channel will have one value (single value) at the end of the measurement
  • Interval value - this channel will have a value for each interval, which we can freely define in seconds.

Please note that custom CA noise or CA noise on the external clock can be also calculated using the FFT filter.