Polycom EF2241 Application Note
Polycom ef2241 audio: reference guide
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Also See for EF2241:
- Programming manual (122 pages) ,
- Application note (77 pages) ,
- Reference manual (68 pages)
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Summary of Contents for Polycom EF2241
- Page 1 How to Choose an Acoustic Echo Canceller Application Note Polycom Installed Voice Business Group September 2004...
- Page 2 Users of wide-band conferencing systems should be particularly interested in using acoustic echo cancellation, as it would allow them to make the most out of the additional audio capabilities of their systems.
- Page 3 (these effects are described in detail later). This degrades the speech that is transmitted, so that the poor audio quality is noticed on the far end. Why not just use a speakerphone? Speakerphones are half-duplex, which means that only one person can talk at a time.
- Page 4 When possible, find out the testing environment as well as the results of the G.167 testing. • Judge audio quality and state machine performance by comparative listening. A panel of several people should listen to the different solutions (preferably the same people, under similar conditions, during a short time span).
- Page 5 • AEC for medium to large rooms - these products may contain microphone inputs and record inputs / outputs in addition to the standard audio inputs and outputs required for AEC operation. • AEC for videoconferencing - these products may contain multiple inputs and outputs, or incorporate “phone add”...
- Page 6 If the product exceeds any of the requirements, this may improve the audio quality to some degree. This improvement, however, will not be as significant as the effects of the tail length and state machine. Therefore, all G.167 compliant devices should be considered equally...
- Page 7 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. This flexibility allows manufacturers to test their products in the types of rooms they were designed for and claim compliance.
- Page 8 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.
- Page 9 AEC and decides if it should be in double-talk, transmit, receive, or idle mode. The quality of the state machine has the most drastic effect on the audio quality of the system, and is what will make the most difference in the perceived quality between one echo canceller and another.
- Page 10 This is where the echo would be heard in the first place and most of the echo canceller’s problems become evident. If the echo canceller is sold as part of a complete system (including microphones and speakers), some evaluation also should be done on the near end to ensure all of the audio components are of good quality.
- Page 11 acoustics have such a large impact. If this cannot be arranged, 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. Seven Things to Listen For •...
- Page 12 Double-talk The state of the echo canceller when there is speech on both ends of the connection. This is the most difficult state to detect accurately, and most problems with audio quality occur during double-talk. Bandwidth The frequency range the canceller passes without attenuation. For narrow-band (telephone) applications, this is defined as 300-3000 Hz.
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Page 13: Technical Support
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