Time evaluation

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With a time evaluation , the time course of a sound pressure level measured with sound level meters or analyzers is filtered with a specific time constant . For digital sound level meters, it indicates how long the waveform is sampled before its rms value is calculated. The set time weighting thus influences the inertia of the displayed or measured level curve .

Standardized time evaluations

In DIN EN 61672-1 3 different time evaluations are standardized:

  • S (slow): time constant 1 s
  • F (almost): time constant 125 ms

and in Appendix C (informative)

  • I (pulse): time constant level rise 35 ms, time constant level fall 1.5 s

With the setting "S" there is thus a strongly dampened time curve of the displayed or recorded level. The level is much more restless in the "F" setting. The setting "I" is characterized by rapid increases in individual sound events and a subsequent only relatively slow decrease. This time evaluation was originally intended to improve the evaluation of impulse-like sound events. According to the information in Appendix C of DIN EN 61672-1, however, it is not suitable for this.

In addition to the time weightings mentioned above, the time weighting "Peak" is specified, in which a very short time constant is used for the level rise and there is no decrease in the displayed level. The peak value in the entire level curve is therefore maintained.

To identify the level, the time constant used is named in the index, e.g. B. L I for pulse weighting. If a frequency weighting is also used, this is also specified (e.g. L Bpeak for B- weighting and time weighting "Peak").

Different time evaluations are used depending on the measurement task. The time weightings to be used are also specified in standards for noise measurement.

Window functions

In a certain sense, the window functions used in digital signal processing are also evaluations in the time domain. In acoustic measurement technology, however, the term "time evaluation" mainly relates to the standardized evaluations of the level curve explained above.

literature

  • Jürgen H. Maue; Heinz Hoffmann; Arndt von Lüpke: 0 decibels plus 0 decibels equals 3 decibels , Berlin, Erich Schmidt Verlag, 2003, ISBN 3-503-07470-8