I have a practical question about echo cancellation and Voip. I have made a 'black box' which contains analogue electronics of a phone earpiece and mic. However i have problems when connected to Voip. This black box is plugged into a major manufacturers Voip device + PC which converts the analogue voice into a Voip signal for input then across the Voip network. However When a far end caller using PSTN, calls through the Voip box and into my black box he can hear substantial echoes of his voice. I know that the Voip will add delay to the system thus any impedance mismatches in system such as my black box will cause echoes. I have tried to alter the impedance of my black box but still echoes occur at far end caller using PSTN. I can place a DSP with adc and dac between my black box and Voip box to perform some echo cancellation. However would this work at that position? or would i need to place the DSP echo canceller somewhere else on network? Hope this diagram helps. ------------------------------------------------------------------ | | | ////////// ///////////// |\\\\\\\\\\\\\\\| //////////// PSTN call------>PC + Voip box | position of | ////////// ////////////// |echo canceller | <---- Black box | DSP ? | analogue voice ///////////////// ///////////// | | ------------------------------------------------------------------- Thanks John Stokes
'black box', echo and Voip
Started by ●June 12, 2009
Reply by ●June 16, 20092009-06-16
>I have a practical question about echo cancellation and Voip. > >I have made a 'black box' which contains analogue electronics of a phone >earpiece and mic. However i have problems when connected to Voip. This >black box is plugged into a major manufacturers Voip device + PC which >converts the analogue voice into a Voip signal for input then across the >Voip network. However When a far end caller using PSTN, calls >through the Voip box and into my black box he can hear substantialechoes>of his voice. > > >I know that the Voip will add delay to the system thus any impedance >mismatches in system such as my black box will cause echoes. >I have tried to alter the impedance of my black box but still echoesoccur>at far end caller using PSTN. > >I can place a DSP with adc and dac between my black box and Voip box to >perform some echo cancellation. However would this work at thatposition?>or would i need to place the DSP echo canceller somewhere else on >network? >Hope this diagram helps. > ------------------------------------------------------------------ > | | | >////////// ///////////// |\\\\\\\\\\\\\\\| //////////// >PSTN call------>PC + Voip box | position of | >////////// ////////////// |echo canceller | <---- Black box > | DSP ? | analogue voice > ///////////////// ///////////// > | | > > ------------------------------------------------------------------- > >Thanks >John Stokes >You should position your echo canceller between the Voip box and the Black box as shown in your diagram. Even though the echo delay caused by the black box is likely short, the voice quality that the PSTN user hears can be very poor due to the long delay through the Voip network (can be tens to hundreds of milliseconds). When the delay is this long even a very small echo sounds annoying. The G.168 spec from the the ITU-T has a lot of info on echo cancellers if you are interested: http://www.itu.int/rec/T-REC-G.168/en Other than the newest (pre-published) version, the spec can be downloaded for free. Its too bad your voip box doesn't have an echo canceller built into it. Shawn Stevenson http://www.linkedin.com/in/sestevenson
Reply by ●June 18, 20092009-06-18
>>I have a practical question about echo cancellation and Voip. >> >>I have made a 'black box' which contains analogue electronics of aphone>>earpiece and mic. However i have problems when connected to Voip.This>>black box is plugged into a major manufacturers Voip device + PC which >>converts the analogue voice into a Voip signal for input then acrossthe>>Voip network. However When a far end caller using PSTN, calls >>through the Voip box and into my black box he can hear substantial >echoes >>of his voice. >> >> >>I know that the Voip will add delay to the system thus any impedance >>mismatches in system such as my black box will cause echoes. >>I have tried to alter the impedance of my black box but still echoes >occur >>at far end caller using PSTN. >> >>I can place a DSP with adc and dac between my black box and Voip box to >>perform some echo cancellation. However would this work at that >position? >>or would i need to place the DSP echo canceller somewhere else on >>network? >>Hope this diagram helps. >> ------------------------------------------------------------------ >> | | | >>////////// ///////////// |\\\\\\\\\\\\\\\| //////////// >>PSTN call------>PC + Voip box | position of | >>////////// ////////////// |echo canceller | <---- Black box >> | DSP ? | analogue voice >> ///////////////// ///////////// >> | | >> >> ------------------------------------------------------------------- >> >>Thanks >>John Stokes >> > >You should position your echo canceller between the Voip box and theBlack>box as shown in your diagram. Even though the echo delay caused by the >black box is likely short, the voice quality that the PSTN user hearscan>be very poor due to the long delay through the Voip network (can be tensto>hundreds of milliseconds). When the delay is this long even a verysmall>echo sounds annoying. The G.168 spec from the the ITU-T has a lot ofinfo>on echo cancellers if you are interested: >http://www.itu.int/rec/T-REC-G.168/en >Other than the newest (pre-published) version, the spec can bedownloaded>for free. > >Its too bad your voip box doesn't have an echo canceller built into it. > >Shawn Stevenson >http://www.linkedin.com/in/sestevenson > > >Hi So essentially i have to model the impulse response of the box and use this as the weights of an adaptive filter. Since these weights adapt to the input can i initially simply model the impulse (weights) as a simple impulse (for example)? thanks john
