Delay in audio with NVFaxDetect

We’ve recently installed an upgraded version of spandsp, version 0.0.6pre3. We’re also using the agx-ast-addons to register the application with asterisk (version 1.4.23). We’ve been able to dramatically increase fax reliability using a SIP only solution. Everything appears to work correctly in the call plan but we are getting a delay in audio when answering the phone when using the NVFaxDetect. If we disable NVFaxDetect via FreePBX then the delay goes away.

I realize this doesn’t have anything to do with FreePBX but was wondering if anyone has experienced this issue and has any advice?


If what you mean is that the phone rings it connects but you hear nothing for 3-5 seconds that that is expected as it’s the fax detext listening to the line for the dialing in line to have the fax tone.

The delay is as you outline but that isn’t the way the freepbx default dialplan works. FreePBX creates the dialplan that answers the call, then does nvfaxdetect (if configured), and if it is not a fax call, hands off the call to continue the dialplan (e.g. follow-me, sip devices, etc). NVFaxDetect should not cause an audio delay for a SIP phone.

The problem is that we are getting that delay AFTER nvfaxdetect finishes listening. So on the asterisk console we see (in a simplified fashion)

  1. Call answered
  2. Call handed to nvfaxdetect
  3. Call detected as not fax after 4 seconds (configured in FreePBX)
  4. Dialparties executed and sip phone starts ringing
  5. Party answers the sip phone and there is a delay of 2-3 seconds.

If we disable NVFaxDetect then everything works normally.