Notes from the Field: On Capturing Video and Audio

Notes from the Field:
On Capturing Audio and Video
Michael R. Chial, Ph.D.
January, 2008
INTRODUCTION
These notes summarize lessons learned over the past three years while attempting to
capture audio and video of adult clients/patients in recording studios, in the field and in often
cramped treatment or conference rooms. Background concepts and suggestions are noted about
camcorders, microphone systems, lighting, and miscellany. Most of what follows focuses on
hardware. Specific products named below have proven their usefulness in the field. No doubt,
others would useful as well, but many alternatives were found to be troublesome (or downright
terrible) and are excluded from mention.
ABOUT VIDEO RECORDING
VHS is as dead as the polyester pants suit. Get over it. To capture quality video, digital
recording methods and media are necessary. Removable recording media are useful for backup
and storage. Digital tape is preferred because there is no compression of data during the
recording process. This is not the case with cameras using recordable optical media (CD or
DVD), or even with some on-camera hard drives.
Two digital tape camera systems are commonly available. One uses Hi-8 (mm) tape and
is essentially proprietary technology (Sony). The other uses mini-DV tape and is arguably the
current semi-professional and professional standard, for which cameras from several vendors are
available. The two types of tape are shown below: mini-DV on the right; Hi-8 on the left. Each
can record about an hour of video.
Because mini-DV tape is common in professional applications, cameras using this
medium are typically (but not always) compatible with add-on professional recording
components, in particular microphones. Why not use the microphones provided with cameras?
Because in most cases they are not very good and because they are ill-suited to much of the
recording we wish to do for serious research or instructional purposes. Such uses (which may
involve transcription, acoustic analyses of speech, or both) mandate good signal-to-noise ratios,
which in turn require (1) quiet recording equipment and environments, and (2) minimal mic-tomouth distances. We’ve found that clients and patients are more likely to tolerate a nearby or
body-worn microphones (e.g., a lavalier mic) than a close-proximity camera with a cameramounted mic.
MICROPHONES 1
Professional quality mics limit the effects of stray electromagnetic (EM) radiation (noise)
on audio recording. This is done using connector and cabling methods with three wires vs. the
two wires found in consumer-grade gear. The third conductor is a shield tied to equipment
grounds at both ends of cables that allows systems to null intruding signals that appear between
the ends of the link. Where does the noise come from? From long cables, from fluorescent
lighting fixture ballasts and from other sources--we are awash in stray EM radiation.
Professional three-conductor mic systems are said to use balanced lines (technically, all pairwise combinations of conductors have equal impedance).
Most professional balanced-line mic systems also employ phantom power, a DC bias
voltage (from 5- to 52-volts) needed for mics based on capacitance or condenser principles. In
part, this is needed to match the high output impedance of such microphones with the lower
input impedance of recorders, that is, to provide pre-amplification. The actual electrical power
for phantom power function can be provided by batteries in the microphone body itself, or (in
professional applications) by internal components of adapters, mic mixers or camcorders
designed for that purpose.
Microphones differ in other important ways, sensitivity, directionality and self-noise
being the most important. These factors, plus different recording purposes and environments,
suggest the need for different mics in different circumstances. One size does not fit all.
ABOUT CAMERA MIC SYSTEMS
Pictured below is a legacy Sony DCR-TRV720 digital Hi-8 camcorder followed by a
close-up of the input/output connections for the camera. The built-in stereo mic of this camera is
suitable for casual recording, but not for serious work because it cannot be placed close to
talkers.
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The 1/8th-inch, three-conductor port shown below in red can accept line-level signals
from two separate microphones, but does not provide phantom power. In other words, the
camera “expects” consumer-grade external microphones. (Line-level refers to a 0 (zero) dB
reference of 0.775 volts, or 1.0 milliwatt at 600 ohms. Yes, this gets technical).
Balanced-line, phantom-powered mics can be used with this type of camera, given a
proper adapter. One such is the BeachTek DXA-6 dual-channel, phantom power adapter shown
below. Cost: about $300.
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This 9-volt battery-powered unit accepts one or two balanced-line, phantom-powered mics via
XLR connectors (see below) and conditions the audio signal for line-level input to a camera like
the one shown above. Each channel has a separate gain control to accommodate speaking level
differences of talkers. An output connector (1/8th-inch stereo plug) can be routed to a camcorder
if the latter has an appropriate line-level input jack. The adapter is designed to attach to the base
of a camera, then to a tripod.
Shown below is a more current and more costly camcorder, the Sony HVR-V1U
DVCAM. This mini-DV camera was selected in February of 2007 following an extensive
review of available professional and near-professional camcorders.
The HVR-V1U provides 48-volt phantom power to two mics, the record levels of which
can be controlled independently. Also, both input lines can be routed to a single record track.
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This camera offers numerous advantages beyond balanced-line, phantom-powered
external audio (e.g., an excellent lens, superior white-balance, focus and iris control; both
standard definition and high definition video; real-time monitoring of exposure, etc.). While
more complex than cheaper models, it has proven flexible in field, studio and clinic
environments.
Audio input ports are provided for balanced-line (three-conductor) connections to mics
(see above). Note the user-supplied blue and red tapes to clarify the two audio channels (red for
right, blue for left). In this image, you can see an unused female three-conductor jack, called a
XLR or Canon jack. This type of connector is routinely employed at the camera end for
balanced-line mics.
Shown below are XLR cable connectors of the sort used with professional mics. The
middle is a female connector; the other two are male connectors. Invariably, balanced line,
phantom powered microphones have male connectors and require a female cable-end connector,
while cameras (or audio mixers) have female connectors and require a male cable-end connector.
Again, note the user supplied colored tape to distinguish among audio channels. One advantage
of balanced line, phantom-powered systems is the ability to run relatively long cables between
mics and cameras.
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MICROPHONES 2
So, there are ways to connect high-quality remote mics to both consumer-level
camcorders and more professional camcorders. But what mics should be used? For which
applications? And at what costs?
At least four scenarios can be identified: (1) one client or patient and one clinician in a
smallish space where the voices of each must be recorded, (2) more than two people conversing
in a smallish space, (3) larger groups conversing in a mid-sized space or studio, perhaps around a
table and (4) special circumstances in which a camera-mounted “shotgun” mic is indicated. In
the examples that follow all mics are phantom powered and use blanced lines, i.e., the tell-tale
XLR connectors.
Solution for Senario 1: Use one lavalier mic for each of two individuals, recording their voices
on different stereo channels with whatever adjustable gain differences are needed to equalize
voice levels.
This is perhaps the most common circumstance. We have had excellent results with the
Shure SM-93 lavalier mic (cost: about $150). This omnidirectional unit (when worn) essentially
becomes a directional mic due to the body baffle effect. The supplied grey foam wind shield is
an effective way to limit sibilent, plosive and breath artifacts. The large black connector shown
below can be clipped to a belt or wiastband and the mic (next to the quarter in the image) can be
clipped to a shirt or blouse. The large connector accepts a XLR cable that can lead to a phantom
power adapter, or to a camera capable of providing phantom power.
Solution for Scenarios 2 and 3: Use a mic boom and a mic with adjustable directionality pattern.
We’ve had excellent results in studios with the Studio Projects C3 mic (below) mounted
on a mic boom (a three-legged telecoping stand with a “fishpole,” a counter-weight and a mic
holder—not supplied with the mic). The mic has switched control of directional pattern from
omnidirectional to bipolar to directional (cardioid). This large-diaphram mic is more sensitive
than smaller units and as a result has greater “reach.” Note the supplied shock-mount holder for
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the mic (the pole is not supplied), an important way to limit spurioius noises associated mic
movement. The black foam cover is intended for windy environments. Cost: about $330.
Solution for Scenrios 2 and 3: Use one or more PZM mics.
This is a common soloution in group therapy situations involving (for example) four to
ten persons. The Audio-Technica U841A pressure zone mic (PZM) offers a design that limits
spurious effects of phase differences of reflected signals arriving from different directions and
with vaying delays. This small mic can be mounted on a 12-inch by 12-inch plate attached to a
tripod, to a wall, or simply placed on a table top. Connecting cables (not supplied with the mic)
are needed for routing to a phantom power adapter, or to a suitable camera. Two of these mics
can be used with camcorders offering two-channel audio; more can be used with a suitable mic
mixer (see below). Cost : about $230 each.
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Solution for Scenario 4: Use a superior shotgun mic mounted on a compatible camcorder.
After trying several alternatives, we found good results with the Rode NTG2 shotgun mic
(cost: about $270). “Shotgun” implies highly directional sensitivity. This mic comes with a
shock-mount (this mates to a receiving shoe on the camera) that mechanically isolates the mic
from the camera. The mic offers better directionality, “reach,” and overall qualtity than similar
mics supplied with otherwise professional qualtiy cameras. The foam cover defeats wind noise
and need not be used indoors.
MICROPHONES 3
“What about radio frequency (RF) systems that place a lavalier mic and small transmiter
on a person and broadcast audio to a receiver connected to a camcorder?”
Most of these are not balanced-line units, although most provide line-level outputs for
camcorders. Inexpensive units (e.g., those under about $400) are prone to self-noise associated
with RF transmission methods. More expensive units function better, but the total cost of good
audio based on such systems may exceed the costs of the options noted above.
“What about more than two mics?”
One solution is to use a mic mixer that can accommodate more than two phantompowered mics. The Fostex MR-8HD has four phantom power mic inputs and an internal hard
drive for audio (only) recording. The level of each mic input can be controlled independently.
Outputs can be mixed to stereo and directed to a suitable camcorder. Cost: about $400.
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AUDIO FOR VIDEO: END NOTE
“Options are nice, but how do I know what works?”
 Get to know your gear. Read the manuals (duh!). Or find a reponsible assistant who
will do so and tell you what you need to know.
 Be sure you have enough good quality cables to connect microphones to other gear. To
the extent possible, keep cable runs short.
 Attend to your intended finished product. Will it use a single mono signal on both right
and left channels, or two different audio signals? If the former, and if your equipment
allows, do any needed signal mixing from two sources at the time recordings are made, or
later during editing.
 It is sometimes best to avoid the automatic audio gain contol function common to
camcorders, particularly when recording patients or clients with low speaking levels
together with normal talkers. Instead, manually adujst audio input levels to get
appropriate results.
 Use good quality earphones connected to your camcorder to monitor and verify what you
capture as you record it. Attend to quality (includling freedom from audible distortion),
not just audibility or loudness. This should be done for each recording session.
 Don’t test mic connections by tapping them with your fingers (would you like to be
tested that way?). Instead, ask talkers to count from one to ten for each audio input.
Make level adjustments as needed. Keep in mind that digital audio is very unforgiving
when over-driven.
LIGHTING SYSTEMS
Although the auto exposure feature of camcorders can control exposure to some extent,
supplemental lighting may be needed to provide even illumination and to avoid excessive
contrast between light and dark areas. A mininmal lighting kit consists of three fixtures, plus
stands to hold them. One instrument is used as key, another as fill, and a third for background.
Lighting kits such as the Britek halogen units shown below produce good results. These
use 300 or 600 watt lamps that give very even color (see below) The movable black wings
(barndoors) help put light where you want it. Many kits come also come with umbrellas and / or
fabric hoods (softboxes) to diffuse illumination, thus limiting harsh lighting that is often unkind
to older subjects. Complete kits (with fixtures, lamps, barndoors and stands) begin at about
$400.
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More cosly (and heavier) are lighting instruments with fresnel lenses, the main advantage
of which is the ability focus light. This is done by adjusting the position of the lamp relative to
the fresenel lens. At least one of these is a good addition to a lighting kit. Cost: about $250.
Recent developments in lighting for film and video include flourescent instruments with
specialized lamps that minimize color temperature problems. These are relatively large,
expensive, and produce more diffuse illumination than halogen instruments. Their central
advantage is avoiding the heat of hallogen lamps, but they require cameras with adjustable white
balance (see below).
Video lighting options range from simple to complex. Simple is best. For more, see
Jackman, J. (2004). Lighting for Digital Video & Television, 2nd edtion, and Braverman, B.
(2005) Video Shooter, both from CMP Books (San Francisco).
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COLOR TEMPERATURE AND WHITE BALANCE
This topic is complicated because it involves interactions among natural and artificial
light, camcorder function and the subjects being recorded. Color temperature is indexed in
degrees Kelvin, with lower values denoting warmer illumination. Most clinic and laboratory
areas are plauged by flourescent lighting and by attendant color temperature problems. In short,
institutional flourescent lighting can make otherwise healthy subjects look positively green (as in
the stageplay Wicked).
Several solutions are possible. Some depend on camcorder features. Many cameras have
color balance presets for sunlight (about 5600 degrees Kelvin) and household tungsten lamps
(about 2900 degrees Kelvin) or halogen lighting (about 3200 degrees Kelvin). None have
presets for institutional or home flourescent lighting (about 4300 Kelvin for cool white lamps).
If the camcorder allows manual calibration of white balance, consider using inexpensive cards of
the sort shown below. Standardized color cards can be imaged by your camera and the camera
white balance can be adjusted to produce the proper color mix, forcing a particular card to appear
white when recorded under whatever lighting exists.
If your camcorder does not allow control of white balance, a screw-in color correction
filter (flourescent to daylight [FLD], shown at the left, below) attached to the objective lens of
your camera may help. This approach is less useful when your subjects are illuminated by
multiple light sources with different color temperatures.
Filters useful for other purposes include a circular polarizing filter (to limit glare from
reflective surfaces such as glass or metal), a neutral density filter (ND 0.6) to mute overall light
level, and special effects filters (e.g., Soft FX 1 and Black Diffusion FX) to mute unattractive
facial features. Color gels for lighting instruments can accopmplish some of the same purposes,
but they are more cumbersome. Similarly, some digital video editing software can correct color
temperature problems in post production, but with greater cost and complexity.
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In any event, you should always use a 1-A sky screw-in filter with the objective lens of
your camera to protect the camra lens and to limit ulraviolet wavelengths of light that might
otherwise challenge or confuse your camcorder. Tiffen manufacures excellent fiters in a wide
range of sizes to fit diifferent cameras.
MISCELLANY
A sturdy camera tipod is absolutely required to avoid jerky images. Tripods with
cameras can be awkward to move. Inexpensive add-on wheel systems, such as the Davis &
Sanford W3 collapsing unit shown below (cost: about $130) allow easy repositioning of almost
any tripod-camera system.
Used correctly, a tripod will limit unwanted camera movements. Even so, problems can
occur while manually panning, or tilting a camera. Inexpensive battery-powered, remote control
pan-tilt units such as that shown below at the left can eliminate this problem (cost: about $190).
Similarly, activating the zoom control on a camera can produce jerky or uneven effects. The
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item shown below at the right is a remote (Sign Video Zoom Commander Pro) for zoom, focus,
record, pause and stop control of Sony, Panasonic or Canon camcorders (cost: about $180).
A common issue in clinic and lab environments is clutter. A simple solution is to mask
clutter with a cloth backdrop hung from appropriate stands. Painted muslin drops are commonly
used in television and photography for this purpose. All of the images above were taken using a
Belle Drape 10 foot by 24 foot muslin drop (#531L). Another good option from the same
manufacturer is basic black (#702L). Muslin drapes range in cost from $50-150 each; a pair of
stands with a mounting pole cost another $140.
One or two tall director chairs (about $100 each) in an unobtrusive color (black) can be
very useful. These place subjects near eye level with standing individuals and simplify camera
positioning and establishing subject eye contact with the camera.
Finally, if cameras and accessories are moved from place to place, consider investing in
protective cases. File storage cases such as that below (available from office supply stores-Office Max or Office Depot) provide adequate safety without adding much weight.
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FROM CAMERA TO COMPUTER
Most current digital camcorders offer a Firewire (called iLink by Sony) connection to
allow uploading recordings to a computer. Doing so can subject a camera to unnecessary wear.
A good alternative is to use a separate playback deck compatible with your tape format. Sony
manufactures such devices for both Hi-8 digital tape (model GV-D800 NTSC) and for mini DV
tape (Model GV-D1000 NTSC). Cost: about $650 and $1000, respectively.
Both units use the IEEE-1394a protocol (400 Mbps) and cables with 4 pins at the
recorder end and 6 pins at the computer end. A faster alternative, IEEE-1394b (800 Mbps),
employs 9 pin connectors. The connector types are not mechanically compatible but cable-end
adapters are available.
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SOURCES
Becoming familiar with product alternatives requires consulting manufacturer web sites.
When products are sold directly by manufacturers, they are often priced at suggested retail costs.
In most cases, you can find better prices elsewhere, sometimes through vendors having discount
arrangements with your institution.
Locating sellers of video cameras and support gear is easy. Just use Goggle. But beware
of uncommonly low prices, often posted by fraudulent vendors, or by vendors who don’t stock
what they claim to sell. To make a phrase, if it looks too good to be true, it probably is.
Reliable vendors offer both competitive prices and reasonable return policies. They also
may offer extended warrantees (mostly useless), but they don’t push them. We’ve had excellent
results with the following vendors.
Adorama (http://www.adorama.com/)
Amazon (http://www.amazon.com/)
B & H photo video (http://www.bhphotovideo.com/)
Full Compass (http://www.fullcompass.com/)
ImageWest.TV (http://www.imagewest.tv/)
Sweetwater Sound (http://www.sweetwater.com/)
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