What is "Dialog Level"?
In most film and television drama production, the dialog is the central element, typically defined as the anchor element. Thus, the sound level of a program is widely connected with the level of the dialog. The idea of keeping the dialog at a constant level throughout the program is to provide stable speech perception and intelligibility. In television (flow-tv), it helps keep the level constant between programs and channels.
The Advanced Television Systems Committee worked out a set of guidelines intended for Dolby AC3 based audio. Initially, the level settings were determined by a rather complex measure of the Dialog Level, providing data for the "dialnorm" (an abbreviation for "dialog normalization)."
The dialnorm data are sent with the program in the form of metadata to provide the receiver's optimal setting. However, after introducing the standard ITU 1770 on Program Loudness, the so-called K-weighting algorithm has been a valid method to generate data on Dialog Level for the dialnorm setting.
Figure 1 K-weighting curve.
The target loudness is defined as -24 LKFS (the K-weighted equivalent program level is -24 dB relative to full scale). The max peak is -2 dBTP (the max level of the true peak in any part of the program is -2 dBFS).
The practical implementation has met some challenges due to various standard options, especially regarding IP-based distribution. So, the Recommended Practice on Dialog Normalization is not followed by all content providers.