Instruction/ maintenance manual of the product OMNIVS500U Polycom
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How to Choose an Acoustic Echo Canceller Application Note Polycom Installed Voice Business Group September 2004.
Introduction Acoustic echo cancellers (AEC) greatly enhance the audio quality of a multipoint hands-free communications system. They allow conferences to progress more smoothly and naturally, keep the participants more comfortable, and prevent listener fati gue.
AEC Nonlinear Processing Mic Speaker Echoes Near speech Far speech Far speech Near speech + echoes + distortion Far End Near End XMT RCV Distortion Figure 1: Illustration of the effects of AEC operation and room acoustics on the transmitted speech. The far speech that trav els through the receive path is not modified as it passes through the AEC.
frequently, if at all. With acoustic echo cancellation, the echo path is very complex (dozens or hundreds of reflections), lasts 100-200 ms, and can vary conti nuously during a conversation as people move around the room. Acoustic echo cancellers are therefore much more complicated devices.
Form Factor The form factor of the solution is very important because it determines how useful it is in an application. The performance of the product may not matter if its fo rm factor makes it inconvenient or impossible to use in the desired application.
Step 2: Eliminate the products that don’t meet G.167 or the tail length needs of the application. It is relatively easy to determine how well an AEC cancels echoes. Most AEC products are based on the same algorithm: the adaptive LMS digital filter. This is a very well-defined algorithm that has been used for years.
Room Acoustics G.167 testing is performed in real rooms. If the product meets the requirements in these rooms, it is compliant. A device that is G.167 compliant in one room, however, might not be compliant in another. This is because the acoustics of all rooms are different.
The equation assumes that both the microphone and the speaker are mounted on the same wall (which is the worst case in terms of the number of reflections that will be cancelled). In that case, N must be an odd integer because the even reflections travel away from the microphone.
Step 3: Judge audio quality and state machine performance by comparative listening. Ideally, the AEC will let speech signals pass through it unharmed. This is actually the most difficult task in both designing and measuring the performance of an acoustic echo canceller.
The two most critical states of the echo canceller are receive and double-talk. The receive state is the only opportunity for the echo canceller to converge correctly. It is also the time when the echoes are most noticeable because they are not masked by speech from the other side.
acoustics have such a large impact. If this cannot be a rranged, at least consider the operating environment differences in each case in the final decision. If possible, listen to the room acoustics with the echo canceller disabled so the effects of the different rooms can be compared.
A Short Glossary of AEC Related Terms Near end The end of the connection where the echo canceller is located. This is where the echoes take place. Also, see far end . Far end The end of the connection opposite the echo canceller. The user on this end could be using a handset or another hands-free system.
Technical Support For support on the Vortex product line, call toll-free (USA/Canada) 888-248-4143, then select option 1, then option 3. For exclusive Integrator and Consultant focused suppo rt (through our PASS program), dial 1.408.474.2048; this number will get you help on video and Vortex products.
An important point after buying a device Polycom OMNIVS500U (or even before the purchase) is to read its user manual. We should do this for several simple reasons:
If you have not bought Polycom OMNIVS500U yet, this is a good time to familiarize yourself with the basic data on the product. First of all view first pages of the manual, you can find above. You should find there the most important technical data Polycom OMNIVS500U - thus you can check whether the hardware meets your expectations. When delving into next pages of the user manual, Polycom OMNIVS500U you will learn all the available features of the product, as well as information on its operation. The information that you get Polycom OMNIVS500U will certainly help you make a decision on the purchase.
If you already are a holder of Polycom OMNIVS500U, but have not read the manual yet, you should do it for the reasons described above. You will learn then if you properly used the available features, and whether you have not made any mistakes, which can shorten the lifetime Polycom OMNIVS500U.
However, one of the most important roles played by the user manual is to help in solving problems with Polycom OMNIVS500U. Almost always you will find there Troubleshooting, which are the most frequently occurring failures and malfunctions of the device Polycom OMNIVS500U along with tips on how to solve them. Even if you fail to solve the problem, the manual will show you a further procedure – contact to the customer service center or the nearest service center
