Download VU Meters to Loudness Meter

From ＂hearing＂sounds to ＂visualizing＂sounds
VU (Volume Unit) Meters and Loudness Meters
Introduction
With the transition of analog TV broadcast to digital TV
broadcast, the digitized production of TV programs, the resulting
availability of wide dynamic range, and the rapid advancement
of audio equipments, the sophisticated sound technology has
become widely used. TV program creators and particularly TV
commercial creators try to increase sound level to attract the
audience. As a result, the sound levels vary greatly between
channels, between programs, or between a program and
commercial break, requiring the viewers to adjust TV volume at
every program or at every channel change.
To reduce the annoyance to TV viewers, loudness meter
measuring human-perceived sound level has been required
instead of conventional VU meter measuring sound level in
electrical strength. Once, there were several sound meters to
indicate human-perceived sound level such as noise meters.
Recently, however, international organizations such as ITU
(International Telecommunication Union) and EBU (European
Broadcasting Union) developed standards that describe how to
measure sound level (ITU BS.1770-2, R-128). Also in Japan, ARIB
(Association of Radio Industries and Businesses) established a
standard called ARIB TR-B 32.
This guide explains briefly about "sound", "volume meter" and
“loudness" to help you to better understand.
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Quick review of sound and types of
G uidance
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Quick Review
Let’s quickly go through what is sound.
In general, sound is a series of compression waves that
move through air (i.e., changes in pressure).
Sound is composed of 3 factors.
❶Sound Intensity (Strength)
❷Frequency (High-Low)
❸Tone
We perceive sounds by detecting vibration with
the hearing organ - the ear. 3 components of
sound are outlined below.
1 Sound Intensity (Strength)
The sound intensity is the strength of compression
waves.
2 Frequency (High-Low)
The high and low of sound is the frequency of
compression waves. Human ear has a range of audible
frequency, i.e., audibility range.
3 Tone
T he tone is a feature that different sounding bodies
(instruments) have different sound tones even at
the same frequency. An instrument produces the
instrument-specific sound including complex frequency
content so that we are able to identify the peculiar
sounds by each instrument.
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loudness meters
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Types of Volume Meters
Volume meters have 2 major types:
❶Measured by vibration (pressure)
・Noise meter
・S ound pressure meter (SPL Meter: Sound
Pressure Level Meter)
Circuit inside VU meter
sensitivity control resistor
Set to 0VU at reference input
rectifier circuit
germanium diode
❷Measured by electrical signals
・VU Meter (Volume Unit Meter)
・PPM Meter
（Peak Program Meter）
・Loudness Meter
The below describes the second type of volume
moving-coil meter
sensitivity of approx. 80μA
damping resistor
control not to overswing the needle
meters. They are generally used for adjusting or
monitoring sound level on recording or broadcasting.
The rectifier in VU meter is a simple circuit with a
diode. VU meter provides wide-range measurement
capability from -20VU to -3VU (dB), by the logarithmic
i Volume Unit Meter (VU Meter）
characteristics of diode at an extremely low input
voltage. The indicator uses a high-sensitivity DC meter
in a range from 80μA to100μA.
VU meter is adjusted to have 300ms response time to a
step signal in a range from –20VU to 0VU. Considering
its slow response time (around 300ms), the meter
tends to ignore short-term sound and to be actually
closer to the human ear's perception of sound level.
Due to those features, VU meter is still one of the most
common volume meters for measuring sound signals.
VU meter was jointly developed by Bell Labs, CBS and
NBC in 1939 for monitoring and standardizing the levels
of telephone lines. The VU meter consists of a high
ii PPM (Peak Program Meter)
sensitivity DC meter and a rectifier circuit converting
Compared to VU Meter, Peak Program Meter, mostly
sound signals from AC into DC.
used in Europe, has shorter response time of 10ms for
monitoring the peak on sounds recorded.
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The needs for loudness meter and
G uidance
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Why We Need Loudness Meters?
Until recently, VU meter and PPM were the only options
available for“visualizing”sound level. Meanwhile,
with the transition from analog to digital sound, audio
technologies are rapidly evolving. As digital sound offers
wider dynamic range in full bit depth than analog sound
and easy-to-operate sound processing equipments such
as limit controller is available, a technique increasing
sound level without significant changes in electrical
signal level is becoming commonplace.
Through these situational changes, the volume
indicated by VU meter is not always matched with the
loudness level perceived by listeners and the limit of VU
meters has become apparent.
Also in broadcasting, digitization brings variations in
volume levels between programs, commercial breaks,
or channels, forcing viewers to adjust volume at every
commercial break or at every channel change.
To address those issues, loudness meter has been
developed to meet demand for accurately measuring
human-perceived volume incorporating not only
electrical level but also hearing characteristics.
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the outline of loudness
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What is Loudness?
Loudness is sound volume based on human aural
Figure 2
Equal-loudness contour ISO226-1996/2003
characteristics.
❷Masking characteristic
❸Time-based characteristic
(Figure 1)
Human aural characteristics are determined by 3
attributes:
Revised
Previous
Sound Pressure Level［dB］
❶Hearing frequency characteristic
Minimum Level
1 Hearing frequency characteristic is illustrated by
an equal-loudness contour described in ISO2262003 (Figure 2) .
Frequency［Hz］
The equal-loudness contour is a curve for which
a listener perceives a constant loudness over the
frequency spectrum, with using a given loudness at
2 Masking Characteristic
1kHz (e.g., 60phon) as reference for comparison. The
The sound occurred right after a loud sound is difficult
curve indicates that low frequency sounds appear to
to be heard by human ear. This phenomenon is called
be less loud than higher frequency and high frequency
as masking effect.
sounds are less stable. The curves are steep in lower
volume, while the curves become flat in higher volume.
Figure 1
3 Time-based characteristic
Short duration sounds are perceived quieter than longer
Sound signal
sounds of exactly the same level. For instance, even
when a speech gives listeners an impression that the
sound level stays the same all the times, the needle
Hearing frequency
characteristic
on VU meter can be swinging. It shows that humanperceived sound level varies by the sound duration.
Loudness meter is a device that is designed to measure
Masking characteristic
the human-perceived loudness by taking account of the
hearing characteristics.
Time-based characteristic
Loudness level
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Types and Standards of Loudness Meter
G uidance
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Types of Loudness Meters
Mainly, there are 4 standards for measuring loudness
level, and loudness meter products complied with those
standards have been developed.
❶ITU-R BS.1770-2／1771
❷EBU Tech 3341／R-128
❸ARIB TR-32
❹ISO532B
❺Proprietary
While ITU-R BS.1770-2 and EBU Tech 3341/R-128 are
international standards,“Operational Guidelines for
Loudness of Digital Television Programs”(ARIB TR-B32)
is Japanese standard established in March 2011 that
was based on ITU-R BS.1770-2.
ITU is the acronym for the International
Telecommunications Union, which is a specialized
agency of the United Nations. EBU is the acronym for
the European Broadcasting Union, which is an alliance
of public service media organizations, with members of
Europe and North Africa broadcasters.
Yamaki LLM-D1012 is a major product complied with
ISO532B.
Those standards are outlined below.
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Standards of Loudness Meters
1 ITU -R BS.1770 -2
the loudness value is averaged on all loudness values
T h i s s t a n d a r d i s f oc u s e d o n h e a r i n g f r e q u e n c y
captured in a whole content. Then, in order to reduce
characteristics.
the effects caused by intermittent sounds, the values
The concept of loudness calculation under this standard
equal or less than -10LU (Relative-Gate) are excluded
is illustrated below.
from the average just calculated. And the resulted value
ITU-R BS.1770-2 also includes the recommendations
is again averaged to derive the final averaged loudness
how to measure audio level for 5.1ch surround-sound
value (Program Loudness).
(LFE channel not included).
Block diagram of multichannel loudness method
Pre-filter
RLB
RMS
Pre-filter
RLB
RMS
Pre-filter
RLB
RMS
Pre-filter
RLB
RMS
Pre-filter
RLB
RMS
2 EBU Tech 3341/R-128
The standard is established by EBU Ploud group for
loudness normalization.
Loudness
Essentially complied with ITU-R BS.1770-2, it defines its
own standard concerning EBU Mode.
【What is EBU Mode?】
EBU meter has 3 measurement modes as below:
K-filter
● Momentary
loudness
loudness
● Integrated loudness
Relative Lebel［dB］
● Short-term
The standard also recommends how to measure
Loudness Range.
Momentary loudness: Integrated over 400ms
●
●
Short-term loudness: Integrated over 3s
●
Integrated loudness: Same as defined in ITU-R
The standard requires including the functions to
Frequency［Hz］
start/pause/continue/reset measuring the integrated
loudness.
Hearing frequency characteristic is approximated by
K-filter being composed of Pre-filter *1 and RLB*2 , as
shown in above.
3 ARIB TR-B32
“Operational Guidelines for Loudness of Digital Television
It also tends to reflect time-based characteristic with
Programs”(ARIB TR-B32) was defined in March 2011. The
the calculation of loudness level by measuring volume
general requirements are conformed to ITU-R BS.1770-2.
with every 400ms intervals. These intervals overlap
by 75 percent (75%: 100:300ms) for the leveling of
Please refer to each written standards for more details.
measured values and a new value is obtained every
100ms. After excluding values equal to or less than -70
LKFS (Safety-Gate) to mitigate effects by silent duration,
*1　Pre-filter: filter accounting for the acoustic effects of the
head. (by +4dB from 1k to 4kHz)
*2 RLB: Revised Low-frequency B-weighting
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