 |
New Technology for Audio Zoom Microphone
While high-power
zoom lenses have been available for many years to enable close-up
images to be acquired from long distances, the traditional shotgun
microphones and parabolic reflectors used to improve the directivity
of sound pickup have always had somewhat limited capabilities
in noisy environments. New technology for an extremely high-performance
zoom microphone system was demonstrated for the first time in
the United States at the recent Hollywood Post Alliance (HPA)
Technology Retreat held in Palm Springs, February 20-22, 2008.
The AudioScope system developed by Norwegian company SquareHead
Technology was described in a paper presented by SquareHead CEO
Vibeke Jahr. The description below is based on the HPA paper and
demonstration and discussions with Mr. Jahr.
 The
AudioScope uses one or more arrays of 300 small microphones, each
mounted in a thin two meter diameter disk that is typically suspended
over the area of interest. As shown in the diagram to the left,
a small wide-angle color TV camera is mounted in the center of
the disk to provide a live video signal to the system control
unit, showing the area covered by the microphone system. The base
station, remote from the microphone array, comprises a signal
distribution unit, a signal processing unit and a storage system.
A video monitor shows the area of interest picture from the camera
and the system operator is provided an intuitive interface with
a track ball to move a cursor around the image and zero in on
the subject of interest. The audio originating from that location
is isolated and amplified and can be clearly heard even in a noisy
general environment.
Although details
of how it works have not been revealed, it is known that the system
uses phase delay and spatial filtering, with massive signal processing
power to provide real-time processing of audio from the hundreds
of microphone elements in the array. Audio characteristics in
the current system are currently optimized for speech rather than
music or wideband audio. As the cursor is moved on the monitor,
the system automatically adjusts the phase delay of the microphones
to isolate the audio from selected subject. For signal processing,
the system at HPA had four high-end Apple computers working in
parallel.
The system has
been demonstrated to work well in large exhibit halls and sports
venues and in outside stadiums with pickup distances over hundreds
of feet. Multiple microphone arrays can be ganged together to cover
even larger areas. In a large and noisy exhibit space at the HPA
event, one could track and pick up the conversation of anyone in
the hall from a remote location and the subject had no idea they
were being monitored. The system is customized for broadcast users
and is being promoted particularly for use at sporting events to
get close up audio from players, coaches, and fans, but many other
uses are clearly possible both for broadcast and other purposes.
One particularly
impressive feature is that picking out of individual "zoomed"
audio does not have to be done live but can be done in replay
later - for any source of audio in the covered area. The system
uses hard disk recording to capture the raw output from the microphone
array, with the associated video picture, for later playback and
analysis.
Key functions,
as described on the SquareHead Web site are:
-
High directivity.
Attenuates audio sources outside the audio focus with up to -30
dB.
- Real-time
zoom. Zoom in on players or regions on the field where the action
is.
- Post-event
zooming for replay. Full functionality in post-processing gives
the producer the freedom to go back in time to capture an incident.
- Multiple
static sound regions. Listen to the comments from the coach-bench.
- Integration
with industry standard cameras and tripods that deliver coordinates
of the camera lens focus and zoom.
- Multi-channel
system for 5.1 surround sound for HDTV.
The AudioScope
is undergoing final development and will be available as a commercial
product in a few months, with an expected cost in excess of $200,000.
As is common for expensive broadcast equipment products it is
understood that the system will be available for rental from a
specialist broadcast equipment company. More information on the
AudioScope is available at http://www.sqhead.com/.
 2008
NAB Broadcast Engineering Conference Summary of Presentations
Check out the papers
that will be presented at the 2008 NAB Broadcast Engineering
Conference in Las Vegas, April 12 -17, 2008. Find registration,
housing or additional information on the NAB Show at http://www.nabshow.com/.
The
March 10, 2008 TV TechCheck is also available in
an Adobe Acrobat file.
Please click
here to read the Adobe Acrobat version of TV TechCheck.
|
|
