[asterisk-dev] Zaptel Echo Cancellation

[Steve Davies]

On 8/3/06, Chan Kwang Mien <kwangmien at asgent-tech.com> wrote:
> Hi,
>
> My test-bed is as follows :
>
> Caller <--> PSTN Simulator <--> Asterisk <--> Callee
>
> The PSTN Simulator is from VConsole and it simulates echo with a delay =
> 50ms. Asterisk PBX is
> equipped with Digium TE400P Card.
>
> I realised that Echo can still be heard at the Callee whether the Zaptel
> MG2 Echo Cancellation is turned on or off.
> However, when the rx gain value = -5 and tx gain value = 0, the echo
> becomes barely audible.
>
> Am I right that Zaptel Echo Cancellation is suitable only to cancel certain
> type of echo ?
> Does anyone have any comments on this ?

The default echo canceller configuration cancels 128 taps of 8KHz
voice - This works out as 16ms of echo cancellation, so a 50ms delay
will not be cancelled, and will require dedicated hardware EC.

Note that 16ms is plenty for most echo sources that occur in a real system.

Regards,
Steve