[Serusers] Re: Echo Cancellation

NEILL WILKINSON neill.wilkinson at btinternet.com
Mon Jul 10 17:34:58 CEST 2006

  I would suggest the use of a good echo cancelling platform too. Look at your echo cancellers characteristics. The important things to look for are compliance to the G.168 standards and a good echo tail - 128ms is good or sometimes quoted in taps - 1024 taps is good.
  International calls have a longer delay for the voice to echo back - this delay is what the taps/echo tail have to work with. Some cheaper echo cancellers have very short tails - 16ms, which may be sufficient to handle echo on national networks, not on international network connections. Cellular networks can also have longer delays.
  For example Digium PRI hardware (there is a new card coming out soon that is better) has a short echo tail, where as Sangoma PRI cards have a long (128ms) tail. Quintum gateways also have echo cancellers with 128ms tails.
  Choose your hardware for connectivity to the PSTN carefully - it can have dramatic effects on voice quality.

Evan Borgström <evan.borgstrom at ca.mci.com> wrote:
Just because you're sending both calls through the same gateway doesn't
mean that your providers upstream gateways don't change depending on the
destination. Your provider could have tens or hundreds of different
vendors depending on where they terminate calls.

Check the ECAN (echo cancellation), VAD (variable audio detection), etc
settings on your ATA or IP phone. Play with the gains (turing down the
tx gain on the microphone can help). Try changing codecs. Buy a book on
how PSTN audio works or speech codecs, do some google searches, there's
LOTS of info out there.


ravi reddy wrote:
> Thanks for your reply
> Here both local calls and international calls are passing
> through same gateway but why iam hearing echo only for international calls
> can you have any idea please suggest me
> Thank You
> Regards,
> Ravi
> On 7/10/06, ravi reddy wrote:
>> Hi users
>> I noticed some strange thing yesterday when i made a SIP-SIP
>> call everytthing was O.K , when I made SIP-Pstn local call its pretty
>> good
>> BUT When I made SIP-PSTN (international) I am Hearing my Voice back at
>> Some
>> stages , I tried for lot of calls but i dont understand where actually
>> the
>> problem is creating ,
>> Can any body please solve this "ECHO" problem
>> Thanks.
>> Regards,
>> Ravi.
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