| ## Loudness Sum
In the example on the left: Loudness bargraphs M, S, I with EBU scale In the example on the right: SPL bargraph Move the mouse accross the display elements to get the corresponding descriptions.
The Loudness Sum instrument shows the combined total loudness consisting of the summed single channels of a signal. This instrument shows up to three bargraphs representing measurements with individual integration time constants. For stereo sources, the L and R channels are summed. For 5.1 sources, the five main channels (5.0) are used for the measurement. The bargraphs available in the Loudness Sum instrument show the following: M (Momentary): Summed momentary loudness measurements of the individual channels using an integration time of mostly 400 ms (acc. to standard). S (Short Term): Summed loudness measurement using an integration time of mostly 3 s and a sliding window (acc. to standard). I (Integrated): Overall program loudness between start and end points. Use the adjustable test time control or manually the Start, Stop and Reset buttons to execute this measurement. The three bargraphs representing these loudness measurements can be activated or disabled individually. For Loudness measurements, two different scale types with different scales are provided: Absolute scale in LKFS or LUFS (depending on the loudness standard selected). Relative scale in LU. On the relative scale, 0 LU corresponds to their target level defined in the selected loudness standard. In EBU R128, the target level is –23 LUFS. In ATSC A/85, the target level is –24 LKFS. –23 LUFS is identical to –23 LKFS. In order to conform to the individual loudness standard used or to other delivery standards, the measured program should read the „Integrated“ target level of this standard. Using EBU R128, it should read 0 LU on a relative scale or –23 LUFS on an absolute scale.
The SPL Sum instrument is only available after the loudness mode "SPL" was selected for the audio group the instrument is in. It displays the summed SPL level of all channels used in that group and can be referenced to a monitoring level, e. g. 78 dB(A) when the studio monitoring system is calibrated. The parameters used for the SPL measurement are set using the "Loudness" key in the "Audio Group" menu.