May 26, 2004
Note: This Field Notice is a legacy Latitude Field Notice that has been converted to the Cisco format so the information would remain available to their customers.
Echo was heard in MeetingPlace meetings hosted on servers where a large percentage of the participants were using PBX phones with headsets. The specific echo heard was a short muffled buzz immediately following speech . This type of echo sounded similar to acoustic echo from speakerphones.
Echo is the result of outgoing speech energy reflected back by the access port into the inbound path with enough delay to sound distinct. Tracking down and controlling echo is difficult because there may be many possible causes. In this case, echo was reported for meetings with a large number of participants from headquarters connected through the Fujitsu PBX and using Plantronics headsets.
Connecting to a MP meeting from an internal PBX phone should be the cleanest method of attending a meeting from a VQ perspective, but this was not the case here. After monitoring live meetings and analyzing their voice captures, certain parties were eventually identified as the being consistently the cause of this type of echo in any meeting they participated. For some reason, their PBX phones introduced additional echo delay in their connections when compared to the other PBX connections, but the delay should still be within limits for the MP echo canceller to handle. However, the echo cancellers were having difficulty converging for these connections, and this resulted in excessive residual echo.
The root cause of the problem for these echo-y parties was determined to be their Plantronics M12 Vista headset amplifier. These amplifiers were misconfigured for the Fujitsu PBX phone. The echo return loss (ERL) value from these misconfigured phones were very poor (< 6 dB) and possibly fluctuated during a call. This caused the echo cancellers to have a difficult time converging to cancel the resulting echo. Normal bi-directional audio was still possible even with a misconfigured amplifier so this masked the problem. When the amplifier was correctly configured to work with the Fujitsu phones, the ERL returned to very good (25-40 dB) values and reasonably stable.
In this specific situation, when a participant's PBX phone connection causes echo, all the other parties in the meeting hear echo of their own voices. The echo sounds like a muffled buzz and is not a distinct echo of the preceding sound. The echoing party, on the other hand, does not hear echo of their own voice but only the echo of the other speakers. This last fact may be used to isolate the echoing party so the problem can be resolved.
The older but electrically similar Plantronics M10 model amplifier also exhibits this problem. This problem may extend to other external parties not on the HQ Fujitsu PBX, such as Nortel PBX in Dallas, if they are also using a Plantronics M10 or M12 headset amplifier.
In a conference call, only one reflecting access port is necessary to cause echo to be heard by the entire meeting. The echo-ing party does not need to speak to cause echo.
Once a particular PBX phone headset user has been isolated as an echo source, check and correct the compatibility slide switch setting on the M12 Vista amplifier to position 5. The compatibility slide switch is located on the left side of the amplified behind the snap on cover. Likely, the misconfigured amplifier was set to setting 3. The 5 setting matches the Fujitsu PBX phone and electrets headset element. The other valid settings 1, 2, and 6 are used for other types of phones such as, carbon, dynamic and Siemens/Rolm, respectively. The settings 3 and 4 are not specifically defined for any phone type, and the Plantronics factory recommends never using them.
If the echo sources are using a non-Fujitsu PBX phone and an M12, refer to the Plantronics documentation or contact the factory to ensure the proper compatibility switch setting for the particular phone.
Notes about headset amplifier deployments:
Before deploying M12 Vista headset amplifiers to new employees or existing employees who will be using a Fujitsu PBX phone, make sure the slide switch setting is set to 5. The occasion amplifier with 3 setting may be due to incorrect default settings from the Plantronics factory.
Check and correct the slide switch setting on any returned units, whether M10 or M12, to the 5 setting if the amplifier will be used with a Fujitsu PBX phone.
For other phone types, check the amplifier documentation or with the factory to determine the appropriate slide switch setting.
The #5 muting/unmuting is still recommended whenever not speaking in order to avoid or to eliminate MP voice quality issues such as background noise and other types of echo. Local mute/unmute is a less desirable alternative.
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