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FXO to PSTN calls - users hear noise

Users hear a noise, like a machine hum (I verified) on calls via FXO to the PSTN.

I've tried the following on the voice-port

no vad

no caller-id enable (a bug a long time age :)

input gain manipulation

output attenuation manipulation

comfort noise

echo-cancel coverage manipulation

I have noted that the Router (2821) is not grounded and am having the customer take care of this. Could this be a possible cause?

Using an analog test set straight into the circuit, I do not hear the noise.

Possible dsp issue? sho dsp error shows no errors.

Thanks!

1 REPLY
Cisco Employee

Re: FXO to PSTN calls - users hear noise

Have a look at this note on Voice Quality issues and common 'noises' heard -

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

A common reason for 'noise' on analogue ports is incorrect companding. If the port is set as 'compand-type a-law' you will get distorted audio. Make sure this command is NOT configured on any analogue ports.

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