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Troubleshooting CTS echo issues


TelePresence echo can be caused by a number of things. To effectively troubleshoot the issue, your TAC engineer will need to know the following:

  1. Who in the call hears the echo? Does the local endpoint hear its own echo? Does the local endpoint hear reverb from the remote endpoint?
  2. Does the echo consistently occur on every call?
  3. Is the echo only between certain endpoints?
  4. Did something trigger the echo (Software upgrade? Endpoint moved?)
  5. Has the room experiencing echo passed CTX certification or a Room Readiness Assessment (RRA)?

Echo issues are often caused by the room environment at the remote site. Reverb can be caused by the audio channel being out-of-sync.

Configuration Issues

1. The first thing to check is your configuration. In the CUCM device profile of the codec itself make sure Acoustic Echo Cancellation (AEC) is enabled. If it wasn't, check it and save/apply the config.


2. Also ensure you have the correct Microphone Count configured in the device profile if you have a CTS-1300.


3. Make sure the Volume on the phone in each room is set to 7; this is the recommended level.

4. If you're experiencing echo on a standards based endpoint (C-series/EX-series/MX-series, E20 and Movi) when natively calling a CTS running 1.7.4 - 1.8.0, you could be hitting a bug (CSCts48847).

Microphone Issues

1. First, ensure that the microphones are cabled correctly. The center mic should be connected directly to the center codec. The other microphones connect to the audio/video expansion box. The below diagram is for a CTS-1300, but is relatively similar for a CTS-3000 (which does not have positioning mics).


2. If the microphones are wired correctly, run a microphone calibration. Do this from the CTS web GUI. Go to Hardware Setup -> Microphones -> Start. From here you will be able to run a microphone calibration


Hit the Test button to begin the mic calibration. The room must remain quiet! The ambient noise levels in the room should be what they normally are (e.g. noise from a busy street is OK if it's normally present). The calibration will take a couple of minutes.


3. In CTS 1.9.0, you can run CTX certification tests from the GUI. Under the same Hardware Setup -> Microphones screen, there is a CTX tab at the top.


From here you can run Reverberation and Noise Level tests. Run each of these tests and record the results.

The reverberation test will chirp at different frequencies and measure the sound decay time in milliseconds.

Reverb Test Decay TimeAction
150 - 300msIdeal
300 - 500msCause for concern. The issue should be addressed.
500ms or moreMay cause significant impact on TelePresence calls.

The noise level test measures the sound pressure in the room at various frequencies in decibels.

Sound PressureAction
Under 36dBIdeal
42 - 50dBCause for concern. The issue should be addressed.
50dB or moreMay cause significant impact on TelePresence calls.

4. To troubleshoot the hardware itself unplug and test the microphones one at a time and make test calls to see what configuration of microphones causes the echo issues. Try each microphone in each port.

Is any one microphone consistently causing the issue?

Is any one port (on the AEB or codec) consistently causing the issue?

Does the issue only occur when multiple microphones are plugged in?

Let your TAC engineer know if the issue follows a particular microphone, port, or neither.

CTMS 1.8.0 - 1.8.3 bug

If you are experiencing reverb issues only on multipoint calls through a CTMS 1.8.0 through 1.8.3, you could be hitting this bug: CSCua92152. The bug is that CTMS is not sending service reports (SRs) in RTCP packets. These are used to calculate jitter buffers and buffer occupancy. Without receiving RTCP SRs, the audio sync won't happen and the relative delay between audio receivers will be heard as reverberation. Under good network conditions (with QoS properly implemented) the problems are less likely to occur. The more jitter we have, the worse the issue will be.

The resolution is to downgrade to a 1.7 release or upgrade to CTMS 1.8.4. If you see your QoS markings on calls are [BE] (best effort), this means DSCP markings are being stripped off somewhere along the media path. You should also fix your QoS implementation which could mitigate the impact.

Resolving Echo Issues

If it's determined there is too much reverb or noise in a room, the issue will have to be mitigated somehow to decrease or eliminate the echo. A common fix for this is adding staggered acoustic paneling to a room so that no bare wall faces any other. Additionally, one can add sound damping objects such as plants

If you have gone through the above troubleshooting and still have echo issues, please collect the results from above and full CTS logs and upload them to your TAC case. Documentation

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