Translation with SYSTRAN Links
Sound intensity of television

To measure to control

What sound intensity?

Sound intensity of television (DT)

The sound is consisted a vibration of the air which puts pressure on the internal ear of the listener. It is characterized by its amplitude and its frequency. The total intensity received by the ear of the listener at a given moment is thus the sum, on the whole of the frequencies used, the squares of the amplitudes balanced by the effect of the frequency considered on the human ear. The coefficient applied to the intensity according to the frequency is determined by the human characteristics of the head and the ear; for the listening of television, it is described by the isosonic curve K (sometimes also named R2LB).

 

The effect on the internal ear is cumulative: the impression of sound intensity does not depend only on the maximum intensity received, but especially on the office plurality of the intensity on the beach of time considered. Thus the measurement of the “peaks” of the aural signal, i.e. peaks of intensity, does not completely give it an account of the feeling tested by the listener: if it is quite possible to note differences in sound intensity in a few tens of milliseconds, it takes a few seconds to assess the trend and to feel an embarrassment of it. However the function “volume” of the remote control regulates only the level of these peaks, which explains why to the same adjustment of television can correspond of the very different impressions, according to the spacing of these peaks. One calls “sound dynamics” the profile of the aural signal, according to whether the beaches of strong intensity are more or less close. A signal presenting a high dynamics is more “ventilated” and less tiring for the ear.

To measure the sound intensity

In August 2010, after several years of work, working group P/LOUD of the European Union of radio-television agreed on a recommendation of measurement of the sound intensity which gives an account of the impression of the listener: it is recommendation EBU - R128 which provides a measurement of the intensity in “LUFS” or Loudness Units Full Scale according to a precise algorithm also described in recommendation ITU-R BS-1770-2 of the International union of telecommunications. Recommendation EBU-R128 fixes, inter alia, the value of sound intensity of all the types of programs (fictions, advertisements, auto--promotions, live programs) to the value of -23 LUFS. Various technical bulletins (EBU-Tech 3341, EBU-Tech 3342, EBU-Tech 3343, EBU-Tech3344) associated with recommendation EBU-R128 specify the technical methodology and parameters to respect in order to reach the value -23 LUFS. 

On each channel (except the channel of the low frequencies LFE says), the algorithm measures the intensity, i.e. he summons on each frequency the squares of the amplitudes, balanced by the coefficient of the curve K related to the frequency considered. The intensities of the various channels, themselves balanced by a coefficient which gives an account of the effect of the channel, are added. The whole is cumulated on the selected beach of time.

Realized on various slipping beaches of time, the operation provides several measurements:

  • the temporary intensity corresponds to the intensity perceived on a slipping beach of 0.4 second; this measurement being more bound for the sound engineers at the time of the stage of mixing of the audio track,
  • the intensity of short time corresponds to the intensity perceived on a slipping beach 3 seconds;
  • the average intensity corresponds to the intensity perceived over the duration of the whole program (of the beginning to its end), by withdrawing silences (i.e. beaches of time during which the intensity is significantly lower than the average).