Knowledge Base: Audio Conferencing

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How does Audio Conferencing work?

In its most simplest terms, audio conferencing works by digitally summing different voice channels. The summed up signal is then sent back to each recipient after subtracting recipient’s own inbound signal from it. This logic is usually implemented using Digital Signal Processing techniques.

What is Echo Cancellation?

Echo is generated when 2 wire to 4 wire conversion takes place in handling of a voice call. If there is a impedance mis-match then part of the outbound signal is reflected back from the 2W to 4W hybrid. This reflected signal is then heard a few milliseconds later by person speaking into a conference and is perceived as echo. The modern day PBXs and conference bridges are designed to cancel some of this returned echo signal. Thiis is done using digital signal processing techniques.

What is Automatic Gain Control?

Automatic Gain Control refers to adjusting the amplitude of the incoming signal to a ‘normal’ decibel level. If the signal is too weak its artificially boosted up. If the signal is too ‘hot’ the signal is scaled down. In either case the adjustment is made automatically and in real time using DSP techniques.

How can I tweak the AGC parameters?

Under normal circumstances the AGC algorithm takes care of the parameters that impact the working of the algorithm. In specialized cases, the designers of the equipment can alter some of the parameters associated with AGC. Please contact XOP Network’s customer support department if you have XOP equipment and have a need for adjustments to AGC parameters.

What is loudest speaker algorithm?

Loudest Speaker Algorithm allows a conference bridge to automatically determine who the loudest speaker is. This is done by computing speech energy in the incoming voice channels. In such cases the conference bridge can send the output from the loudest speaker to all other recipients as part of the conference mixing algorithm instead of performing raw summation of all voice channels.

Does XOP Networks equipment support DNIS based conferencing?

Yes, XOP Networks bridges support DNIS based conferencing. Our bridges detect the dialed number and the caller id of the person calling in. Based on that information we can allow a person to join a conference without requiring this person to enter a PIN.

How much disk space is required for audio conference recordings?

The sampling of an audio signal is done based on Nyquist theorem. That means our equipment samples an audio signal 8000 times per second. Each sample is then encoded with 8 bits. This implies that for each second worth of audio we need 8000 x 8 = 64,000 bits. Therefore to store 1 hour worth of audio we will need to store 64,000 x 3600 = 230,400,000 bits or 28,800,000 Bytes or approximately 29 MBytes.

What is HD audio conference?

HD stands for High Definition. A HD conference makes use of voice signals that are encoded using G.722 codec. XOP equipment supports use of G.722 codec.

Can I use my USN with a General Dynamic’s Sectera wireline terminals?

XOP USN-16 supports 16 analog FXO ports. This particular model works with a number of Crypto’s including General Dynamic’s Sectera equipment. The Crypto equipment receives encrypted audio from the Defense Services Network (DSN) switch and converts it to a regular audio signal

What is the significance of JITC?

JITC stands for Joint Interoperability Test Command. In United States, DISA/DoD have strict guidelines for products that are used in the Defense Switched Network (DSN). A product has to go through rigorous Information Assurance and interoperability testing to make sure that there are no vulnerabilities that can be exploited for fraudulent use. DoD has established test centers where such testing takes place. After a product has passed all relevant tests it is granted JITC certification and is also placed on DoD’s Approved Product List.

XOP Networks USN-16 Release 4.3.1 with 16 FXO ports is JITC certified.

What is an asymmetric audio conference bridge?

Normal bridges are symmetric bridges. For example, USN-48 is a 48 port symmetric bridge and uses 48 conference resources to place upto 48 people in a single conference. In a asymmetric case, the number of ports are less than number of conference resources. For example there can be a bridge that has 48 ports but 96 conference resources. The additional resources are then used for creating conference of conferences. This functionality is needed in case of hoot-n-holler application where a supervisor/monitor needs to listen to output from multiple active bridges.

What is Hoot-n-Holler conferencing?

Hoot-n-holler conference allows a person to ‘hoot’ that is then heard by all on the other end of the line. This half duplex process continues as long as hoot-n-holler conference is in progress. This type of conferencing is used on stock trading floors and junk yard auctions etc.

Why is IP based hoot-n-holler conferencing important?

Large companies are rolling out worldwide MPLS networks to allow voice and data networking to their globally distributed locations. Companies that are involved in mission critical activity would like to enable quick conferencing over their IP based network assets instead of using leased lines. These saves significant Opex Dollars as mission critical conferencing is only needed during specific occasions such as satelite launches etc. XOP Networks IP based hoot-n-holler fits the bill in such situations. People located in different parts of the globe can get into a always on hoot-n-holler conference simply by lifting their IP phone or a analog phone connected to a FXS to IP media gateway.

What is mission control conferencing?

Mission Critical Conferencing is used in Ait Traffic Control Towers, during satellite launches etc. Multiple teams of individual participants need to be able to jump in and out of conferences very quickly. Typically such control activity is performed by pressing mechanical keys on keysets (CPE equipment) that are located in front of the user. XOP Networks has developed innovative web portal equivalent of such keysets. The web portal can be accessed either on a typical PC or via special touch screen based tablet computer connected to the LAN. A user can access any room simply by touch the particular room on the screen.

What is a command and control web portal?

XOP Networks has developed as special command and control web portal called CCVIEW. This is typically used in mission critical conferencing application. This portal can be accessed from any PC connected to the LAN or via remote access through the Internet. The portal allows a moderator to monitor multiple conference rooms. The moderator can also have talk/listen access to a given conference room. In order to use this system, the moderator first dials into the bridge and gets connected to the CCVIEW. Then from there he/she simply can excersize monitor or talk/listen functions by pressing buttons available on the web portal.

How can I change amplitude of a caller on a conference call?

XOP Networks conferencing equipment supports Automatic Gain Control (AGC). The AGC logic automatically adjusts the level of the signal up or down before the signal is fed to the audio conference mixer. Most modern PBXs also provide a similar function. In case additional tuning is needed for special customer needs, XOP Networks engineers can make adjustments to the AGC paramaters via remote access. In most cases the default settings for AGC are adequate.

In case a participant wants to lower or raise the amplitude of the signal outbound from the bridge, he/she can press ‘7’ to lower the amplitude, ‘9’ to raise the amplitude and ‘8’ to go to the default state.

I hear echo on my audio conference. What can I do about it?

Please ask your participants to stand at least 4 feet apart. Sometimes the audio from a participant gets coupled through a fellow participant’s mouth piece and creates artificial echo. If you are wearing a headset then lower the volume of the inbound audio. If you are using a speakerphone, make sure you use a model that does a good job of echo cancellation.