Averaging (Sound and Vibration Measurement Suite)
December 2007
NI Part Number:
372416A-01
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The Octave Analysis VIs support the following averaging types:
Linear Averaging
Linear averaging is computed by integrating the square of the filtered signal over a fixed time interval and dividing by the time interval. Linear averaging starts when the lowest fractional-octave filter settles.
Exponential Averaging
Exponential averaging is a continuous averaging process that weights current and past data differently. The amount of weight given to past data as compared to current data depends on the exponential time constant.
The following block diagram shows a VI performing 1/3 octave analysis in the 20Hz–20kHz range using fast exponential averaging.
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Note In order to use exponential averaging, you must wire the exp avg settings parameter to a control or constant. |
Equal Confidence Averaging
Equal confidence averaging is exponential averaging with a specific time constant set for each individual band. Each time constant is set so that the standard deviation of the band power measurement equals the confidence value in decibels that the equal confidence level [dB] control specifies.
Peak-Hold Averaging
In peak-hold averaging, the largest measured level value of all previous values is returned for each band until a new value exceeds the current maximum. The new value becomes the new maximum value and is the value returned until a new value exceeds it.
Resetting the Filter and Restarting the Averaging Process
The Octave Analysis VIs reset the fractional-octave filter the first time the VI executes. You can use the reset filter control to programmatically reset the filter. After the filter is reset, a transient response occurs while the filter settles.
You can use the restart averaging control to restart the averaging process without resetting the filter. Restarting the averaging without resetting the filter avoids the transient phase associated with the settling of the filter.
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