FAQ-G.1: What do the level values displayed by the SONAPHONE mean?

Signal processing in the SONAPHONE outputs different sound levels, which are significant depending on the application.

As a basis, raw level values are obtained from the filtered raw data with a sample rate of 1 ms. The derived level values are calculated and stored in much larger time intervals. The sample rate can be varied in the menu "Measurement settings" between 4 ms and 128 ms. It should be noted that the set sample rate has an influence on the representation of data in the spectrogram.

Level values are:

  • L(t) – Instantaneous Level
    The instantaneous level is derived directly from the raw level values and averaged according to the sample rate setting (between 4 ms and 128 ms). For better readability on the display of the SONAPHONE, the largest value out of 8 consecutive values is represented.
  • LF(t) – Instantaneous Level with Time Weighting
    The standardized Instantaneous Level with Time Weighting (also Fast Level) is exponentially averaged with a time constant of 125 ms. The Fast Level follows the physical measurement effect relatively slowly. In history, it has been used on pointer instruments and fast changing measurements to increase the readability of the values.
  • Lmin - / Lmax - Minimum / Maximum Value of Instantaneous Level
    This level is the minimum or maximum value of the Instantaneous Level L(t) (sample rate between 4 ms and 128 ms).
  • Lpk - Peak Level
    The Peak Level is based on the highest measured value in the raw data (sample frequency 256 kHz / sampling time 4µs). It should not be mistaken for the more averaged Maximum Value of Instantaneous Level (Lmax) - the Peak Level can be a few decibels above Lmax.
  • Leq – Equivalent Continuous Sound Level
    The Equivalent Continuous Sound Level is a standardized averaging level and is used to describe time-varying level values. It averages the sound energy over the measurement period according to specific rules.
    It should be noted that due to averaging important information regarding frequency distribution or changing values over time are lost. Therefore, the Equivalent Continuous Sound Level is particularly meaningful when acoustic situations with similar characteristics are compared.

The level values Lmin, Lmax, Lpk, Leq are calculated from the data from the beginning of each measurement and shown on the display. Pressing the "Reset" button in the Levelmeter App will start a new measurement with newly calculated level values. During data recording, the values apply to the recording period.

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