In Broadcast - July 2016 - 74

www.inbroadcast.com | Vol: 6 - Issue 7 | July 2016

InForm

Audio Measurement
For Broadcast TV
Broadcast sound is a vital ingredient to maximum viewer enjoyment, writes Anthony Wilkins,
International Sales & Marketing Manager, Jünger Audio...

ith broadcast technology
evolving at a seemingly everincreasing rate, the video element
of the experience often takes
precedence. The transition from SD
to HD is now more or less complete
and further enhancements in
the form of UHD, be it 4K (or
even 8K) have been successfully
demonstrated and usable hardware
is now commonplace. Just visit
any electrical retailer and the
majority of TV receivers are now 4K
compatible. In the midst of all this,
we should be careful, of course, not
to forget the part that audio plays in
broadcast.
Audio Criteria
So, if you are creating or processing
audio for TV broadcast, what are
the criteria that you should keep in
mind to ensure maximum viewer
enjoyment? An obvious starting point
should be the subjective quality of
the mix itself. In order to reliably and
repeatedly judge this, along with your
preferred set of monitors, a correctly
calibrated
listening
environment
should be considered essential. When
mixing TV content, general consensus
suggests that a measured level of 79dB
SPL (using C-Weighted Pink Noise) at
the mixing position is appropriate. A
monitoring control unit that allows
individual speaker level and EQ is ideal
for this.
Another
element
of
critical
importance these days is the perceived
loudness level in order to comply
with the relevant local standard.
This requires the use of a loudness
measurement based on ITU-R BS.1770
with its inbuilt K weighting and relative
gating to give a reliable reading in
LUFS/LKFS and can be used as a visual
guide to check that the integrated
or programme loudness value is in
line with the target value. Equally
important is to monitor the loudness
range (LRA) of the mix, which whilst
there are no specific targets specified,
should be maintained at a level

HD Video is often accompanied by 5.1
Surround Audio but many consumers
will be watching on equipment that
can only reproduce 2.0 stereo audio.
Here is where DOWNMIX comes in and
instructs the decoder how to distribute
the six channels of audio across the
available two. Finally, DIALNORM is
used to implement a scaling factor
in the decoder that will normalize
all audio output to a loudness level
equivalent to -31dBFS. When used
correctly, this will ensure that all
programmes are perceived as having
a consistent loudness level but it is
dependent on the actual programme
loudness and DIALNORM values being
accurate. All of the above means that
there are multiple opportunities for
inaccurate metadata parameters to
cause unwanted audio effects for the
viewer, and a method of verifying the
values before broadcast would be
advantageous.

will come from an increased
channel count typically by the
addition of overhead "height"
channels. Several proponents
have successfully demonstrated
broadcast compatible systems
based on 5.1.4 or 7.1.4 layouts
where four overhead speakers
have augmented the traditional six
or eight floor-level speakers. This
creates a "3D" sound image where
the viewer or listener is immersed
in audio in all dimensions. Object
based audio will give the end user
the option to personalise their
experience by selecting from a number
of audio sources and controlling the
level and maybe even the position
in the mix. In object based audio,
an "object" is essentially an audio
stream with accompanying descriptive
metadata. The metadata carries
information about where the engineer
placed the object in the mix and at
what level, and is used to re-create,
or render, the audio experience for
the end user. Objects may be static
and placed at a fixed point in the mix
(for example dialog) or dynamic where
they are panned across the threedimensional soundscape (maybe a
plane flying overhead). Depending on
restrictions and limitations decided
at the point of content creation (and
signalled in the descriptive metadata),
the end user could select which audio
source(s) they want to hear from an
on-screen list and perhaps vary the
level at which they are reproduced.

Immersive Sound
Finally we need to have an eye
on the future. The next generation
of audio formats will offer the
possibility of a more immersive
experience along with a degree of
personalisation. Greater involvement

All of this will mean new
measurement tools and test methods
to ensure that the new emerging
audio formats can be incorporated
into existing production and broadcast
infrastructures. But that's for another
article...

Vital Element: programme loudness

appropriate for the final destination of
the content. Wall mounted flat panel
TV's and smaller portable devices in
noisy environments will not be able
to reproduce large LRA values in the
same way that a correctly installed
home cinema system could. As a
guide, for TV broadcast an LRA of 1015LU would generally be considered
acceptable. Again, a well-specified
monitoring controller ought to provide
these features.
Decoder Control
Although not necessarily always
true, it is common practice that the
audio portion of HDTV Broadcasts
is encoded into one or other Dolby
format, be it AC3 (Dolby Digital) or
E-AC3 (Dolby Digital Plus) and this
introduces another consideration,
that of Metadata. When the Dolby
bitstream arrives at the end user's
decoder, metadata parameters will
determine some of the behaviours
of the decoder and how it will impact
the actual reproduced audio. Of all
the possible metadata parameters,
of prime concern are the 3 D's,
DRC, DOWNMIX and DIALNORM.
DRC is a selectable Dynamic Range
Control profile that will apply a predetermined amount of compression
that is useful for matching wider
dynamic range content to equipment
less capable of reproducing the full
range. It is also becoming more and
more commonplace that broadcast

Audio Control: Jünger Audio X*AP

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