Abstract :
Recently, the advent of all digital broadcast centres and transmission methods, such as those employed for the Thames Television NICAM stereo service, has freed the constraints on overmodulation. At the same time, modern circuit techniques, combined with recent auditory research, have made it possible to produce a reasonably simple loudness meter, with repeatable and stable readings. Exactly why a PPM or Vu meter cannot measure loudness level is because the ear adds together spectral components of sounds in a different way to the electrical root mean square (RMS) which is fundamental to the PPM or Vu. In the case of a wideband noise, after using appropriate filtering, an RMS meter can be used in order to give a level indication, in which case, it is called a sound level meter. It is, however, inaccurate to use or call such a meter a loudness level meter, and to find out why this is so one has to delve deeply into both psycho-acoustics and physiology
