The ITU has now officially published an update to its Recommendation specifying "Algorithms to measure aduio programme loudness and true-peak audio level". This specification, casually referred to as 'ITU 1770' forms the basis of the loudness work around the world.
Gating to improve loudness measurement
The main improvement in this second revision of ITU-R BS.1770 is that there now is an explicit 'loudness gate' included. This is the same kinnf of gate gate that is already featured in the EBU R 128 Loudness Recommendation . This gating method has some distinct advantages: for users, because it operates on all types of programme material (classical music, pop music, speech, sports, drama, and so on), and for manufacturers, because it simple to implement, and, like ITU-R BS.1770 itself, royalty-free. Actually it is one of the EBU's PLOUD Group's contributions to the ITU. The EBU PLOUD Group now intends to update the EBU R 128 specification by lowering the gating level to -10 LU (currently set at -8 LU), to bring the gate completely in line with the gating level described in ITU-R BS.1770-2 . The relative gate makes sure that quiet periods, below a given threshold, are left out from the Loudness measurement, because human perception of how loud a programme is chiefly determined by the loudest passages - the so-called 'foreground sound'.
EBU Mode
The EBU recommends that loudness is measured and normalised according to the methods described in EBU R 128 , which builds on ITU-R BS.1770. To help make sure audio engineers use the same meter settings, the EBU has defined the 'EBU Mode' in its Loudness Metering specification (EBU Tech 3341). This helps make sure users are referring to comparable Loudness measurements.
Virtually all major vendors of metering equipment have participated in PLOUD and implemented EBU Mode in their products. There are also many non-metering tools complying with the EBU's loudness work, including tools to normalise audio files for example.
For more information on Loudness, see the Loudness section on this website.