16
AUDIO LEVELS NORMALIZING
This chapter explains in brief the necessity and methods of performing loudness normalization.
WHAT ACTUALLY HAPPENS IN AIRBOX WHEN NORMALIZING?
▪
Performing a level shifting
AirBox
does not process the source sound internally. It normalizes the loudness of the whole programme (file-based playout channel) by adjusting the
audio levels. For example, if there is a source file with average programme loudness of
-32 dBFS
, it will be increased with
9 dB
in order to reach the
referent -23 dBFS specified in the
AirBox
output settings.
▪
Keeping track of the maximum true peak level of the audio.
If the maximum true peak level exceeds
zero dB
, there will be a clipping introduced. If the maximum true peak level exceeds the specified value in the
AirBox
output settings,
AirBox
assumes that the source content is not prepared in a good way by the sound engineer. In such case,
AirBox
will not
reproduce the relevant media source.
Let us follow the latter example with the source file having average programme loudness of
-32 dBFS
. If the maximum true peak level of this file is
-8
dB
, increased with
9 dB
the peak will jump to
1 dB
(above zero). Exceeding the zero will cause clipping. And exceeding the maximum permitted value
(by recommendation:
-1 dB
) will cause skipping the playback of such source.
PLAYBOX WORKFLOW
▪
Loading playlist
▪
Reading the *.MTD file, created by the
QCBox
tool for reference
▪
Reading the relevant audio metadata values, described into it
▪
Based on the loudness metadata,
AirBox
performs a correction of the audio in order to reach the referent
–
23 LUFS (-24 LUFS for US). The
value is configurable through the output settings.
OVERVIEW
The normalizing functionality is developed in accordance with EBU Technical Recommendation R 128. It
is designed to benefit our clients with the intention of:
▪
Performing monitoring and control over the perceived loudness of audio sources.
▪
Reducing loudness differences between programmes. This is applicable when the nature and content
of the audio material(s) changes frequently. For example, such problem most commonly occurs at the
breaks for advertising: there is a jump between audio levels.
Loudness jumps between broadcast channels and between programmes within the same channel are
frequent source of audience complaints. Using the normalizing functionality, the audio levels between
separate programmes will be equalized. EBU Rec. R 128 is based on ITU-R BS.1770 and defines a new
way of metering and normalizing audio. It also recommends some of the following standards:
▪
“
The Programme Loudness Level shall be normalized to a Target Level of -23 LUFS. The permitted
deviation from the Target Level shall generally not exceed ±1 LU for programmes where an exact
normalization to Target Level is not achievable practically (for example, live
programmes)”
–
EBU Rec.
R 128
▪
“
The Maximum Permitted True Peak Level of a programme during production shall be -1 dBTP (dB True
Peak)
”
- EBU Rec. R 128
According to EBU Tech3343, there are two ways to achieve loudness normalization for the consumer:
▪
The first one is concerning a normalization of the source itself, so that the programmes will be
“equally
loud by
design”.
