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ISR 4331 Voice Quality Issue - Hissing


We replaced a 2811 gateway with a new 4331 ISR router and voice quality is terrible.  Information  -


Code - isr4300-universalk9.03.14.00.S.155-1.S-std.SPA.bin

Voice Interfaces - Both T1 PRI and POTS line via FxO

CallManager Version 10.5, latest patch

Gateway Protocol - Issue occurs with both H323 and MGCP

Show Controller T1 shows no slips or errors for the PRI

Protocol - Both G.711 and G.729


The scenario is that voice quality on the IP Phone side of a call hears hissing and noise throughout the call but especially when the IP Phone side is speaking.  The hissing and noise can be heard as the call is being processed in the gateway.  Real weird.  We used a real blanket config (h323) and got these results.  Anyone else experiencing this?  Suggestions?





Greg Cording

Might be worth checking if VAD is in use during a call, VAD generates background noise (comfort-noise or hiss) to fill silent gaps during calls.



TCC_2 posted "How to confirm that VAD is enabled and how to disable it on Cisco IOS gateways" this some years ago..



To confirm whether  Voice Activity Detection (VAD) is enabled on a call-by-call basis, perform these steps:


  1. Make a call.
  2. Issue the show call active (brief) command.
  3. Check the values for the Voice over IP (VoIP) call leg.

To disable VAD, perform these steps:


  1. Confirm that the correct dial peer is being matched.
  2. Issue the no vad command under the VoIP dial peer.





Our resolution was updating the IOS on the gateway.  What version are you running right now?  I will get with our engineer to identify the exact version we applied.

The version we applied was - isr4300-universalk9.03.14.02.S.155-1.S2-std.SPA.bin

I wouldn't say our issue is so much a hissing, more like garbled voice when one party is talking.  Its incomprehensible what they are saying.  However it seems to match the other changes we made, going from 28xx router to 4331 with the new FXO card.

We are currently running:

boot system flash:isr4300-universalk9.03.13.05.S.154-3.S5-ext.SPA.bin

Cisco IOS XE Software, Version 03.13.04.S - Extended Support Release
Cisco IOS Software, ISR Software (X86_64_LINUX_IOSD-UNIVERSALK9-M), Version 15.4(3)S4, RELEASE SOFTWARE (fc3)

I'll try a new IOS and report back.  On a side note, what are all the additional files when I do 'show flash:'?  Are they necessary files for the newer XE OS?


I have the same problem, even using "no vad" command.

What I know is that some old Cisco phones like 7940, doesn't support G722 codec.

 If this codec is forced on your CCM, you have to apply on your router a profile to forcé other codecs supported by old phones:

voice class codec 100