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Sentences are front-end clipped with VAD


Core Issue

Voice Activity Detection (VAD) can cause front-end clipping.


To see if Voice Activity Detection (VAD) is causing front-end clipping, disable it by performing these steps:

  • For Cisco IOS  H.323 gateways:   
    1. Confirm that the correct dial peer is being matched.
    2. Issue the no vad command under the Voice over IP (VoIP) dial peer.
  • For Cisco CallManager and CallManager controlled gateways (such as Skinny Client Control Protocol (SCCP) and Media Gateway Control Protocol (MGCP)):   
    1. Select Service > Service Parameter > Select Server > Cisco CallManager.
    2. Set these parameters to False:      
      • SilenceSuppressionSystemWide
      • SilenceSuppressionWithGateways

If VAD is causing the problem, perform these steps:

  1. Reduce the music-threshold signal level at which voice is detected.
  2. Increase the voice vad-time.
  3. If neither of these tuning techniques work, it is recommended that you disable VAD on the gateways and Cisco CallManager.

For more information on matching inbound dial peers, refer to Understanding How Inbound and Outbound Dial Peers are Matched on Cisco IOS Platforms.

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