REVISTA DE RADIODIFUSÃO - VOLUME 03, N° 03
The Use of Ambience in Broadcast Audio
Daniel Littwin, director New York Digital, member AES
São Paulo, Brazil
June 2009
This article will explain some of the general ideas and specific techniques for using
ambience in live broadcast audio that the author has developed over the past 30 years in the
television industry. The paper is concerned with stereo sound fields. The use of ambience
in a surround matrix is similar in approach, though it of course involves the perspective of
front/back in addition to left/right.
Introduction
Whether one is mixing music, drama, or sports, the same basic techniques and formulae
apply. The specific microphone choices and placements change, as do the tonality and
processing choices. However, regardless of the event, the need to maintain a consistent
audio field remains important.
For sports, the transitions are spontaneous and instantaneous in order to keep the onscreen
action emphasized to coincide with the game. For music and gala events, audio transitions
are determined by musical scores and scripts. In all cases, the audio portion of the
production is determined by the visual presentation. Audio is a way to engage the viewer’s
attention and to draw them into the presentation, and, importantly, to keep them interested
enough to pay attention to the advertisements. Many studies have indicated that audio is a
very important component of television and that viewers have greater interest in shows with
better audio. 1
As audio gains in importance, technology ensures the cost benefit. Multi channel audio
transmission can be implemented at only a small increase in overall transmission costs. 2 As
consumers continue to purchase televisions with better audio components they grow to
expect broadcast audio signal quality comparable to the fixed media that is available:
cinematic releases on high quality DVD’s and video games. 3 These films and games have
large portions of their budgets devoted to audio; both in terms of the equipment used and
the time involved in production and postproduction. 4
1
“Television Sound and Viewer Perceptions,” (with Ann N. Crigler, and V. Michael
Bove) Proceedings of the Joint IEEE/Audio Engineering Society Meetings,
Detroit Michigan February 1991.
2
Dr. John Emmet EBU TECHNICAL REVIEW – October 2002
3
Dr. John Emmet EBU TECHNICAL REVIEW – January 2003
4
NASCAR 2005: Chase for the Cup Designer Diary #3, Jesse James Allen interview By Staff, GameSpot Aug 23, 2004
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Fixing location in a sound field for the home viewer
Hearing and vision work together to form our orientation in space. 5 TV coverage,
especially audio, can and should take advantage of this physiological characteristic in
conjunction with the physics of sound to strengthen the viewer’s sense that they are in the
theatre or arena, experiencing the live event.
Television is generally presented from one point of perspective, ostensibly the viewpoint
from one position in the audience. For live music and gala events, this position is usually
about 2/3 of the distance from the stage to the rear of the audience, in the center. For
televised sports, this position is usually the announcer booth or cabin. These perspectives
are enhanced with other camera angles to improve event coverage. Notable exceptions are
teledramas, presentations “in the round,” golf, and track and field. Establishing a stable
sound field is an integral part of presenting a realistic picture that gives the viewer a sense
of being at the actual event.
To establish an audio perspective for the home viewer, one should use a stereo coincident or
near coincident pair. This article suggests using a matched pair of cardioid condenser
microphones in an ORTF 6 configuration (two matched cardioid capsules set 17cm apart, at
an angle of 110 degrees 7).
= 110º
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
17cm
Figure 1
Personal experimentation with X/Y, mid/side and other stereo arrays, has led the author to
believe that the ORTF pattern seems to best mimic human hearing while being the most
usable in a live broadcast setting. Other stereo reproduction systems also work very well,
but can be unwieldy due to their size or configuration. The Jecklin Disc 8, audio dummy
heads, 9 the Decca Tree, 10 and other systems are all excellent for true stereo pickup, but all
are too large or too awkward to use in a typical live broadcast setting. The pair needs to be
unobtrusive while accurately producing a true left/right stereo image.
Mid/side
microphones are excellent for their monaural summing characteristics but require a
decoding matrix to establish any stereo imagery. In addition, high quality bidirectional
microphones are often significantly more costly than cardioid microphones of the same
quality. X/Y arrays necessarily have a lot of audio information common to both channels
5
The Anatomy and Physiology of the Ear and Hearing, Peter W.Alberti, Professor emeritus of Otolaryngology, University of Toronto
Office de Radiodiffusion Télévision Française
7
http://www.sengpielaudio.com/DasStereo-MikrofonsystemORTF.pdf
8
http://www.josephson.com/tn5.html
9
http://www.neumann.com/?lang=en&id=current_microphones&cid=ku100_description
10
Audio Engineering Associates, Decca Tree manual
6
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due to the proximity of the capsules. AB or spaced omni pairs require very careful
placement 11 and work better with a fixed source rather like an instrument or an orchestra
than with a general sound field. Additionally, mono compatibility may be an issue. 12
The viewer should be able to discern a change in sound as the attention shifts across the
video image from left to right. The use of an ORTF pair assures this change in real
perspective.
The use of a stereo array with distinct and discrete channels is preferable for transmission as
well. When left/right signals have less information common to both channels, the
transmission exhibits a clearer image in the home. Multichannel decoders employ phase
differential sensing to steer mono signals such as the announcer mix to the center channel. 13
The use of an ORTF pair provides sufficient left/right separation and signal differentiation
to ensure center channel isolation and therefore greater intelligibility in center channel
sources.
Another advantage of using an ambient soundfield, as the basis for a broadcast mix, is that
sudden changes to the mix are masked and the overall timbre and level of the mix remains
consistent. Thus, a more proactive mix is possible, giving the home viewer greater detail
and thereby holding their interest to a greater extent, particularly in sports coverage.
This consistency also allows for an apparently louder on-air signal and a more balanced
presentation of commercial breaks. Research has shown that people get annoyed and
complain when the perceived audible level of the commercials is louder from that of the
program. 14 Certainly, it would be easy to reduce the level of the commercial, but it is
important that the overall network sound levels be on a par with all the other networks. 15
Additionally, advertisers would not be pleased if their product weren’t proclaimed at a level
equal to or louder than that of their competition. The use of ambience can help the mix
engineer maintain a louder apparent audio level. The tonic quality of the commercial
breaks is sufficient to ensure that the breaks stand out. Differences in level are not desirable
and should be ameliorated.
Large amounts of time for what is essentially postproduction techniques such as remixing
and reconfiguring taped segments and creating pieces that are acoustically compatible are
not always available during the set up of a live event. Nonetheless, it is certainly possible to
present a spatially coherent sound image thereby ensuring a presentation that is cohesive
visually and audibly. If the program will include live replays with audio, submixes
including the ambient soundfield can be routed from group, auxiliary and multitrack busses
of the mixing desk to the routing switcher and hence to the video recorders, ensuring that
transitions to and from live action are seamless. If the program will require further
treatment in a postproduction setting, then the same techniques apply: stems should be
recorded at unity gain along with the various submixes and individual channels that are
required for post.
11
http://www.recording-microphones.co.uk/spaced-omnis-stereo.shtml
http://www.prosoundweb.com/article/print/better_recording_microphone_techniques_to_produce_warm_spacious_stereo
March 11, 2009, by Bruce Bartlett
13
http://www.tvtechnology.com/article/20352
14
Broadcast Committee of Advertising Practice (BCAP) Consultation on
Sound Levels of Television Advertisements 25 May, 2007
15
Dr. John Emmet EBU TECHNICAL REVIEW – January 2003
12
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The sound field provides all the information necessary to give a live event locality. Not
only do the ambient microphones capture the tone and emotion of the building and crowd
but phase information is presented as well, providing the psychoacoustic connection with
the video image. In order to make the focal point of the program "more present” in the mix,
whether it is announcers or performers, a combination of equalization, compression and
limiting can and should be used to increase intelligibility, apparent loudness and to control
peaks. The same processes can be used to separately control and enhance other specific
sounds in the mix. Combining equalization, dynamics processing and the use of ambience
with judicious attention to metering can ensure that the program material will not be audibly
overwhelmed by commercial breaks. Such practices logically also lead to overall network
audio consistency.
Sports:
The illusion of being in the announce booth or cabin
As previously stated, the visual perspective of most televised sports is generally the
announcers’ viewpoint. In order to create the effect of putting the viewer in the cabin next
to the announcers, place the ambience microphones in proximity to the talent. The
ambience microphones should not “hear” the announcers, but the arrival time of the
ambient noise at the crowd microphones will be the same, (or almost the same), as at the
announce microphones. After ascertaining correct polarity and orientation of the pair, the
audio and visual perspectives will be in alignment. Because the ambient sound arrives at
the announce microphones at virtually the same time as at the ambient pair, the announcers
appear to be in a stereo field, at the game, thus giving the home viewer the audio illusion of
sharing the space with the talent.
Integrating ambience and action
In general, when working within an ambient sound field, the action microphones are mixed
as monaural point sources, panned around the center, in the same left/right orientation as the
ambience microphones. The degree of pan or distance from center is somewhat arbitrary,
subject to the taste of the engineer and production staff, however it should be consistent
with the left/right orientation of the main ambience pair.
Some examples
Basketball
When broadcasting a basketball game, the announce booth is set courtside, at about the
centerline. The ORTF pair is positioned at the announce table, opposite the talent, facing
play and oriented towards a region in the crowd where there is no public address system.
As play moves back and forth across the court the sound shifts from left to right, following
the primary camera. The effects microphones (a lavaliere mounted on each backboard
behind the basket, and shotgun microphones on each handheld camera) are often not panned
at all, or panned very slightly and used as point sources.
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5
Basketball Court
Figure 2
American Football
American football places the announce cabin in the stands above midfield. Four to six
manned mobile parabolic reflectors positioned around the field on the perimeter are
employed along with various shotgun microphones mounted on field level cameras. These
microphones are kept as monaural sources or may be processed through a stereo
synthesizer. The ambience microphones maintain the live “feel” of the crowd and the
event, granting perspective and size. The action microphones bring the viewer into
immediate and intimate contact with the game on the field.
Football Field
at midfield ~ 30 – 40 meters above field level
Figure 3
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Soccer
American soccer coverage is based upon American football coverage. This makes a certain
amount of sense as the same stadiums and fields are generally used for both sports. Often
there are only two parabolic reflectors used, placed on the far side of the field with near side
coverage being handled by shotguns mounted on the handheld cameras. Microphones are
also placed in each corner, behind each goal and on each side of the centerline. Other
microphones can be placed in proximity to the team benches and possibly taped to the goals
themselves. The ambient pair is located in the announce booth. The size and scope of the
event is transmitted to the home viewer while the announcers and game specific audio
events are clearly heard as well.
Figure 4
Tennis
Tennis is viewed end on, in television. The announce cabin is located in the stands at one
end of the court. The ambience microphones are placed here. The action microphones are
panned to the left and right limits and mixed as stereo pairs. They are placed (in pairs)
behind each baseline and mounted beneath the umpire’s chair and on each camera on either
side of the net. A lavaliere is laced into the net and treated as a mono source. As the
players move from side to side the positioning and motion is quite apparent. This reality of
image truly holds the viewer’s attention and enhances the live viewing experience.
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Tennis Court
Left Side
Right Side
ORTF Pair in Announce Booth located
in the stands at the end of the court
~ 15-25 meters above the court surface
Figure 5
Left to right perspective in sports is determined by the primary camera angle, which also
determines the placement of the ambience pair. The positions of the action microphones
and the use of panning are dependent upon the specific sport and the aesthetics and
experience of the mix engineer. Consistency in left/right orientation is also critical in
maintaining signal phase, an important consideration for transmission and program
reproduction. The ideal mix is a balance of ambience for size and perspective, close
microphones for immediacy and specific play action, and of the announcers clearly heard
yet situated inside the arena.
However, it is also important to keep in mind that certain images are generally shown with
no particular Left/Right orientation. The goalie in soccer is one such example. Most often,
the goalie is viewed head-on. Therefore panning of the goal microphone should not be
extreme. Many other similar examples can be found. The challenge lies in creating a
realistic stereo balance that coincides with the video presentation.
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Live Music and Gala Events
The ambient pair is the means by which the mix engineer can place the home viewer in the
theatre, in the audience. These microphones also serve as a natural reverb, recreating the
sound of the hall with virtually no effort.
Orchestral and big band music is generally panned as viewed by the conductor. The
ambient pair must agree with this orientation. The main orchestral pair is located above the
conductor’s head. All section microphones and soloist microphones are treated as monaural
sources and integrated into this spatial scheme. The ambience pair follows the left-right
orientation of the main orchestra pair. This pair provides the depth and reverberations of
the concert hall as well as audience reactions. All microphone orientation needs to be
consistent with the primary camera angles.
Other music forms: pop, rock, and commercial music in general, are also panned for
presentation in camera perspective, though culturally we expect a less exaggerated pan
scheme overall than is presented by the orchestra. Here it is a matter of the experience and
taste of the engineer and production staff. The greatest part of the left/right orientation
typically comes from the ambience pair.
Drama
Here again, the ambience pair is used as a means to place the home viewer in the audience
and to act as a natural reverb. Most modern drama presentations utilize wireless
microphones. Shotgun and front-of-stage mounted microphones are also used. These are
generally treated as dialog and kept in the center of the mix. If stereo (or surround) sound
effects are employed, they should be pre-edited to coincide with the camera perspective and
the ambient pair. As theatrical sound and sound effects generally coincide with lighting to
create locality in the theatre, this normally is not an issue. Live theatrical music is generally
presented as one would an orchestra or other musical group.
Surround
It is even more important to maintain discrete channels when working in a surround matrix.
Surround, of course offers the opportunity to add front and back perspective to the left/right
image. This is easily accomplished with a secondary ambient pair. A second matched pair
of microphones should be placed far enough away from the “front” ORTF pair so that
arrival times of sounds are significantly different between the 2 pairs. These rear ambient
microphones could be another ORTF pair or 2 discrete microphones placed equidistant
from the front ORTF pair. This establishes the size of the surround image, unifies the
overall image integrity, and ensures that discrete channel information is presented to any
encoders and decoders. 16
Signal compatibility is a common issue facing broadcasters presenting surround
programming. Many choices have to be made based on signal composition, available
transmission paths, and other factors affecting origination, transmission, and reception.
16
http://www.tvtechnology.com/article/20352
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For stereo reproduction of a surround matrix, it is generally advantageous to drop the rear
and LFE channels completely and to recombine Left/Center/Right in correct proportion for
stereo output. If crucial audio information is present in the rear channels, for example,
specific action related effects or instrument microphones, they must be downmixed into the
stereo signal. In the author’s experience it is often better to create and monitor this
downmix manually, rather than rely on the mixing desk’s convergence matrix, metadata and
the encoder/decoder thus ensuring that the stereo program presented in the viewer’s home is
the same as at the point of origin. There are times of course, when a separate stereo mix
cannot be transmitted. In these cases, careful monitoring of all mixes and modes must be
done through the decoder. All of this further exemplifies the need for maintaining discrete
signals.
Surround presents many challenges to an engineer, especially in a live milieu. An accurate
mix image requires proper mix room set up, which is complicated by the need for correctly
matched and oriented speakers mounted in an acoustically balanced space. In the case of
most video trucks, this is a difficult challenge in the space allotted. Encoding and decoding
the metadata is critical. The audio equipment necessary for creating the stems and various
outputs for total signal compatibility must also be available. Maintaining a stable
soundfield by relying on ambience removes several critical variables and makes a difficult
job much simpler.
Summary
Ambience is a part of the environment. Our spatial orientation depends upon our
correlating sonic ambience and visual information. Mix engineers can take advantage of
this physiological characteristic by the use of ambience to create a soundfield in which to
mix the program.
Maintaining a consistent left to right perspective is critical; both in terms of maintaining
consistency with the video image and keeping the audio image clear of conflicting
information that can cause listener fatigue and encoder/decoder problems.
The use of phase coherent ambient pairs with discrete channel characteristics creates a
stable soundfield and ensures that transmission paths are not adversely affected by
encoder/decoder sets, and that spoken word communication is clearly intelligible.
Ambience can mask abrupt changes to the mix balance, a normal occurrence in live
broadcast audio, particularly in televised sports and dramatic events. This allows the mix
engineer to provide the home viewer with more specific and immediate audio details by
faster anticipation and reaction to the events being presented.
Surround imaging demands even greater attention to phase and maintaining discrete channel
information. The use of ambience improves the sound and simplifies the effort.
Ambience enables a more consistent overall audio level throughout the network program
list. Commercial breaks can therefore seem more like part of the programs into which they
are inserted. The inherent difference in tonic quality will ensure that the breaks stand out.
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The audio level consistency will ensure that the home viewer is at least more willing to
listen to the information being presented.
The use of ambience helps to maintain consistent imagery and creates television programs
that sound more like the human experience and are therefore more inviting to the home
audience.
There is no substitute for actually being at a live event. However, with the ambient
soundfield conveying the tone and emotion in the stadium or theatre and the effects
microphones (for sports), or the music and dialog mix (for gala events) providing intimacy
and proximity, a visceral connection is made for the fan at home, increasing their interest
and enjoyment, and hopefully their loyalty as a viewer.
Cite this article:
Littwin, D.; 2009. The Use of Ambience in Broadcast Audio. Revista de Radiodifusão. ISSN Print: 1981-4984. ISSN Online:
2236-9619. v.3. doi: 10.18580/radiodifusao.2009.3.59. Web Link: http://dx.doi.org/10.18580/radiodifusao.2009.3.59
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