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Polycom Video Communications Polycom Video Communications
Advanced Audio Technology for Video Conferencing
Connect. Any Way You Want.
Author:
Peter L. Chu
September 2004 2
If you ask frequent users of video conferencing
technology what they consider to be the number
one product feature for providing a high quality
video conferencing experience, their response
will most likely be the requirement for excellent
audio. High quality audio is far more important
to the perceived quality of a video conference
as dialogue, discussion and decision making are
usually the most important elements between
meeting participants.
With an undisputed leadership role in the audio
conferencing segment, Polycom also takes the
leadership role with our outstanding audio
quality in video conferencing systems. It is
Polycom's goal to create and provide video con-
ferencing solutions that deliver the highest
quality audio capabilities for any environment.
With Siren 14 and now patent pending
Polycom StereoSurround audio technology,
Polycom once again raises the bar for quality
audio standards and delivers true performance
to our customers.
Polycom's leading advantage: Siren 14
Polycom's Siren 14 technology brings 14 kHz
audio fidelity for the most natural conversation.
With twice the fidelity of other vendors, and
four times the fidelity of a telephone call,
Polycom is the only company in the industry to
offer such "super-wideband" audio capabilities
for video conferences.
With 14 kHz audio in a video conference call,
participants can better hear and understand
each other, while eliminating the fatigue often
associated with longer duration calls under
inadequate audio quality.
Why Siren 14 Audio is Important
Speech information is usually contained in the
100-11,000 Hz range, so having frequencies
above 11,000 Hz is not important except for
music. While a small minority of people can
hear up to the limit of 20,000 Hz in audio
frequency, the large majority of people cannot
hear the difference between 14,000 Hz and
20,000 Hz high frequency limits for even the
most demanding music material. The Siren14
codec in the iPower 9000 and VSX 3000, VSX
7000 and VSX 8000 provides audio capability
up to 14,000 Hz, allowing for transparent
reproduction of both speech and music.
The Siren 14 algorithm suite, developed and
patented by Polycom is designed to provide a
scalable wideband audio solution that will obviate
any reason to use narrow band (3.4 kHz) audio
coding. When combined with Polycom patented
audio echo cancellation, the suite provides an
environment that allows both the local and
remote speaker to engage in conversation
simultaneously, without cutting each other out.
Siren 14 operates at 14 kHz audio at bit rates
between 24 and 48 kbps, the usual bandwidth
allocated to audio transmission in a video
conference. Polycom's unique Siren 14 Super
wide band audio capabilities provides incredible
audio quality approaching compact disk and
MP3 quality, while maintaining a modest network
bandwidth requirement. In comparison to other
audio algorithms, such as MPEG 3 and MPEG 4
at lower bit rate transmissions, Siren 14 actually
delivers a smoother and more superior sound. 3
Polycom's Digital Tabletop Microphone: A natural
companion for Siren14
Most video conference systems use simple
directional microphones. Typically these micro-
phones have a (+/- ) 45 degree pickup pattern as
measured from the axis pointing from the front
of the microphone. The disadvantage of this
type of microphone is that participants who are
sitting away from the pickup pattern cannot be
heard as well as those sitting closest to the
microphone. Polycom digital tabletop micro-
phones deploy technology that allows for voice
pickup in a 360 degree radius covering distances
up to 10 feet away from the microphones.
Polycom digital tabletop microphones also use
background noise suppression functions which
eliminate unwanted background noise such as
that generated by laptop or projector fans and
vents. The benefit of automatic noise suppression
creates a virtually noise-free communication for
most meeting environments.
By using Polycom's digital tabletop microphone
technology combined with the Siren 14 audio
algorithm, conference attendees can sit anywhere
in the room without having to worry whether
their voices are being heard at the remote sites.
An example of this capability is exemplified
within the tabletop microphone shipped with
the VSX 7000 product series. The VSX 7000
tabletop microphone deploys a three element
microphone array that forms a narrow beam that
automatically points to the person speaking. The
narrow beam eliminates noise and reverberations
from other directions.. When several microphones
are linked together, the microphone nearest the
person speaking is automatically and seamlessly
chosen while noise from the remaining
microphones is eliminated.
Audio Reproduction from Polycom
Equally important to participants in a video
conference is sound fidelity of the speakers that
produce the audio signals. Clear speech, after
all, is noted as one of the the most important
elements of a video conference. Often, end users
rely on the quality of television speakers for video
conference audio reproduction. These speakers,
however, are not well suited for reproducing
speech, the most commonly transmitted audio
signal in video conferencing applications.
Television speakers are usually designed to offer
merely adequate audio reproduction for a low
price. As a result, these television speakers often
sound similar to a portable stereo system.
Polycom offers custom high fidelity audio
speaker systems to provide the highest quality
speech reproduction for video conferencing.
The VSX 7000 is the world's only set-top video
conferencing system that includes an integrated
speaker and companion subwoofer to provide
near CD-quality audio in any setting. The Polycom
Executive Collection offers a 270 Watt speaker
subsystem with each Executive Collection con-
figuration; ideal systems for this configuration
include the Polycom iPower 9000, VS4000
and VSX 8000. Polycom also provides an auxil-
iary Speaker Kit, ideal for adding Polycom
StereoSurround capabilities to the VSX 7000 or
VSX 8000. This Speaker Kit consists of a sub-
woofer with 150 watts output power with two
6-inch drivers with bass response down to 35 Hz
and dual speakers that include a 3/4" silk fabric
dome tweeter combined with two 3 1/2" compos-
ite midrange drivers for superb sound reproduc-
tion at frequency ranges of 100 Hz to 22 kHz.
The Total Polycom Audio Solution
With all of these great audio technologies, it is
easy to see why Polycom's audio is the best in
the industry and why Polycom continues to be
the market leader in video conferencing solutions.
Setting a new standard: Polycom Stereo
Surround
Consumers are used to enjoying stereo audio
when listening to music, watching DVD movies,
or even experiencing impressive multi-channel
audio at movie theatres. Stereo makes the overall
multimedia experience more realistic and less
fatiguing, providing us the required spatial cues
to separate out different sounds. On a video
screen, when someone on the left hand side of
the screen talks, we expect that sound to come
out the left side, and stereo allows this to happen.
In our everyday life, we are used to having
sounds come from all directions. In mono con-
ferencing, when every sound comes from a single
point in space, it is very artificial and fatiguing.
To make stereo audio conferencing a reality,
Polycom has developed breakthrough patent
pending technology for the VSX 8000,
VSX 7000, VSX 3000, and other products. The
technology includes stereo echo cancellation,
Automatic Gain Control (AGC), noise suppres-
sion and audio compression technology.
Diagram 1: Area pickup of Polycom Digital Tabletop microphone compared to other microphones. 4
Echo Cancellation: The Enabler for Polycom
StereoSurround
If stereo audio is so ubiquitous in the consumer
industry, why it is absent in the video confer-
encing industry? The problem has to do with
echo cancellation. Echo cancellation is required
to eliminate the pickup of the loudspeaker by
the microphone. Without echo cancellation,
users would hear feedback which would make
the conference very annoying. Conventional
echo cancellers identify only one path between
the loudspeaker and the microphone. In stereo,
there are a multiplicity of paths between the two
loudspeakers and microphone, which confuses
the echo canceller. To solve this problem, many
researchers have resorted to distorting the left
and right loudspeaker signals, which enables
correct estimation of the multiple paths.
Unfortunately, this distortion can often be
heard, especially for music.
After a decade of research, Polycom has
developed patent pending stereo echo canceller
technology which doesn't distort the signal, yet
quickly identifies the multiple paths of the
stereo loudspeakers and eliminates echo,
allowing for full-duplex conversations. There is
no "white noise" training sequence, as found in
competitor's mono echo cancellers. Positioning
of the loudspeakers and microphones is not
critical. If microphones are moved, the stereo
echo canceller quickly adapts to the new posi-
tion within one or two words of speech. For the
frequency range from 50 Hz to 14,000 Hz, the
echo canceller adaptive filter length is 160
milliseconds which is adequate for even large
rooms of 30 by 50 by 9 feet in dimension.
The ec