building intercom voice cuts in and out

[dan.letkeman]

Hello,

I have a few locations where I have building intercom systems connected to fxo ports on our srst routers for local paging from phones.  It seems to be working alright for one way audio (paging into the hallways or into all zones).  When we intercom from the phone to the room and want to do two way audio the voice going from the phone to the room speaker cuts in and out.  The voice going from the room mic back to the phone sounds fine.

Could this be something that I could fix on the router or would this be an intercom problem?

Only relevent config I have added to the router to make it work is this:

voice-port 0/0/1

output attenuation -3

description Building Intercom System

!

dial-peer voice 500 pots

destination-pattern 4480

port 0/0/1

forward-digits 0

Thanks,

Dan.

[Jesse Drohen]

Do one way pages to the room that has two way issues work fine?

Do two way pages work to other rooms without issue?

[dan.letkeman]

Jesse,

Thanks for the response.

I did some more testing and found out that its happening in the same fashion at all of the locations, and it doesn't matter what brand of intercom, so that leads me to believe its something with the voice equipment.

No two way page works properly.  The person on the phone side speaking into the room always cuts in and out.  Reguardless of the room or brand of intercom.  One way pages seem to work fine anywhere.

Something to do with the voice codec or voice activation?

Thanks,

Dan.

[Jesse Drohen]

How are users in the room communicating back to the phone? Is there a mic on the speaker or is there some sort of handset? It almost sound like when someone puts you on speaker and try to talk from across the room, that never sounds good.

You could try to input the gain on the port but I think it will just lead to louder bad quality.

[Rob Huffman · Accepted solution]

Hi Dan,

It sounds like "clipping" to me. Have you ever used a speaker phone when listening to

a presentation and the words cut in and out. This is because of the room noise causing

the mic to think someone is speaking and "clips" the incoming voice signal. I'm guessing

the mic in the rooms where the two-way is being set up is causing the same effect.

In my example, if you mute the mic then the incoming voice doesn't cut in and out anymore

so you'd need to change the intercom to somehow work that way. Is there a half-duplex

config setting?

http://telecom.hellodirect.com/docs/Tutorials/DuplexExplained.1.080801.asp

There are some notes on clipping and VAD in this tech note;

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_white_paper09186a00801545e4.shtml#clip

Cheers!

Rob

"Everything is broken" - Bob Dylan

[dan.letkeman]

That does make sense now, becuase when they use the handset that is dedicated for the intercom they have to hold in the button when they want to speak.  That means when they are holding the button they are initiating the mic to turn off in the room, then no clipping occurs....

So what I need to find out, is can I have them hold in a button when they want to speak....I'll go try this shortly.

[dan.letkeman]

I will have to find a way to re-configure the intercom to require the user in the room to press the button to speak or find out a way for the phone to use a button to mute the remote microphone in the room when you want to speak in order to fix this problem.

Unless there is a way to adjust the sensitivity levels to a point where it works....unlikely.