In Broadcast - November 2013 - 30

I N T E R N A T I O N A L

WWW.INBROADCAST.COM | ISSUE 25 - NOVEMBER 2013

N E W S

InREPLY

ZEN And The Art Of Loudness Metering
Chromatec pioneered the first widely used product to measure loudness
based on research carried out by Thames Engineering in the 1990s.
NuMedia Managing Director Stuart Sommerville answers our questions...

I n B ro a d c a s t : W h e n w a s
Chromatec Video Products
formed and what were its ﬁrst
products?
Stuart Sommerville: Chromatec was
formed in 1994 by audio enthusiast
and business entrepreneur Michael
Stevens, originally based in Bromley,
Kent. It was set up to design and
manufacture a range of pioneering
audio and video metering products.
The AM-2 was the ﬁrst product
designed that allowed two channels
of audio levels and phase to be
superimposed on a through-going
composite PAL or NTSC image with
alarms displayed in-picture and
simultaneously output on GPIO lines.
Subsequent products expanded
the number of inputs supported
and modularised the design.
Support for IP based alarms
monitoring was offered and
Chromatec loudness was added
with the advent of digital video.
Later developments saw the same
high quality metering introduced into
a range of modular multiviewers.
InB: What is loudness
measurement and why was it
introduced?
SS: Viewers initially highlighted
programme loudness as a problem
during commercial breaks. Despite
the introduction by the Independent
Broadcasting Authority (IBA) of
recommended peak levels for
different types of programme
content, viewer complaints
persisted. Further tests at the
IBA conﬁrmed that the problem
did not necessarily correspond
to a peak level indication but that
perceived loudness is dependent
on both amplitude and frequency.
In late 1993, the
Independent Television
Commission (ITC) engaged
Thames Engineering to
design a loudness meter
and produce prototypes
for assessment. Working
with John Emmett at
Thames and Charles
Girdwood at ITC,
Chromatec engineered
the prototypes which were
successfully evaluated
in several locations and
later shown at IBC in

Figure 1 Comparison of Chromatec and BS1770 Loudness Contours.

1994. Channel 4 were one of the
ﬁrst users of Chromatec loudness
metering and used it extensively
throughout their facility, as well as
several of their advertising providers.
In 2006, the ITU released BS.1770,
specifying the algorithms used to
measure subjective programme
loudness, and true-peak signal level.
InB: How does Chromatec
loudness differ from R128/ITU-R
BS.1770?
SS: There are several differences
including the frequency weighting
curve as shown in Figure 1.
The Chromatec loudness meter
was limited to two channels but
BS.1770 allows for surround
channels to be included.
In some respect, Chromatec
loudness more closely resembles
R128 short-term loudness because
there is no audio gating and the three
second sliding rectangular time
window is similar to the Chromatec
four second attack and decay time.
Whilst the unit interval is the

same for both types of meters,
where 1 unit is 1dB, the Chromatec
loudness meter is a relative scale type.
For R128, both relative and absolute
scales are deﬁned. The units used
for relative scales are LU and for
absolute measurements it is LUFS.
But perhaps the main difference is
that BS.1770 allows for an Integrated
loudness measurement that can
be used to verify compliance of a
complete programme.
InB: Do Chromatec products
support ITU-R BS.1770?
SS: Absolutely. All Chromatec
loudness metering products support
the latest version of BS.1770-3
but most products also support
Chromatec loudness which is still
used as a reference standard with
some content providers.
InB: What are Chromatec's
loudness products?
SS: The MD-16 and IPM-16 are
both fully featured in-picture audio
metering products supporting the
display of

embedded audio (or optional
external audio) as vertical bar
graphs superimposed on throughgoing video. They provide an
effective in-picture alarm system
for both audio and video errors.
Two EBU R128 compliant
loudness meters may be displayed,
with each one allowing up to ﬁve
channels to contribute to the
loudness levels. The MD-16 card
which is currently offered in the
openGear modular format, can be
used as a stand-alone device or in
multiples to form a multi-channel
system with external control and
alarms reporting via the openGear
Dashboard application. The IPM16 exists as a stand-alone miniconverter with HDMI output and is
conﬁgured via USB connection.
InB: What are the key features
of Chromatec's audio metering
products?
SS: Chromatec in-picture meters
are designed to efficiently
convey accurate level and
loudness
measurements.
Accuracy is assured by upsampling the audio to 192kHz
using the guidelines provided in
BS.1770-3 to obtain an estimate
of the maximum true peak level. The
loudness measurements are carried
out at the incoming sample rate
with an overall loudness tolerance
of +/- 0.1 LU. Following BS.1771
recommendations, peak level
meters are displayed separately from
loudness meters to avoid confusion.
Loudness meters may be reset,
paused and restarted again using
the control interface. This affects
both the integrated loudness
and loudness range
measurements,
thereby
allowing the
loudness
and
the
accumulated
duration of a
programme to be
measured.
InB: Thank you
for taking time
to answer our
questions.

MD-16 card for openGear and standalone IPM-16-EXT mini-converter

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