Audio Issues in external and internal calls


Hello everyone.

I currently have an UCM6302( with the latest firmware), and around 25 GRP2604P( with the latest firmware) phones distributed between 3 offices.We have been informed that within the last 3 weeks there have been audio issues during calls between extensions and with external numbers.The audio problems have been described as choppy or “as if the speaker were far away”, audio delay is also present.
This problems don’t happen at all times but are frequent.
This set up has been running correctly for a year.

I will try to share a picture of how the network is currently distributed, but in words:
the router is a Unifi USG-Pro 4 it has a downlink(CAT 6) to a Cisco SG300.
The Cisco SG300 is in Office 1, and has to downlinks(Fiber) both to switches Unifi one on Office 2 and another on Office 3

Thanks in advance for any help.



Please disable the below options in all the extensions.
Under Media option

  1. Audio FEC
  2. Video FEC
  3. Jitter buffer

And Select the few codecs as mentioned below under all extensions and IP phones as well.

Please try it and share your feedback.


will do, also it seems after the firmware update on all phones and ucm the only remaining issue is audio delay


when I do the configuration in the ucm the extensions dont update the changes, I had to manually enter to each extension and change the set up, but the options are different on the phone web ui; I can’t turn off jitter buffer there’s only two options adaptive or fixed.
The “audio fec” option doesn’t exist on the GRP2604P, there’s another one called “enable audio red with fec”


probably the options indicated are on the UCM and not on the phone,
Have you opened a Grandstream support ticket?


the issue is similar to the one described in here:

Same UCM and Phone models, and around the same time period but I have the latest firmware, I disabled “enable audio red with fec” and the issue seems to be gone, I’ll keep an eye out to see if the problem persists.

I have another site with a similar issue and time period but 2601P phones instead of the 2604P, I will try on a small group of phones the same setting and see how it goes.



These are in UCM–> Extension/Trunk—>Extension----> Edit All SIP
1. Audio FEC
2. Video FEC
3. Jitter buffer
4. Codec= PCMU, PCMA, G729


Config In IP Phone:
Account–> Codec>
Enable: Use First Matching Vocoder in 200OK SDP


Try on telephone:

P8563=0 [Enable Headset Noise Shield]
P8538=0 [Enable Handset Noise Shield 2.0]
P26073=0 [Enable Audio RED with FEC]


Yes I made these changes, and I checked that every extension had the same codecs.

thank you, so far it seems everything its okay.



I added this P26073=0 [Enable Audio RED with FEC] on the other project I was mentioning, it did work the audio delay seems to be gone, this were a different model 2601P.
Thanks for the help.