GSM Telit GL 865 Dual V2 acoustic echo cancellation with AT command?

[kcagiran]

I am working on a device that makes voice communication between machines and human. But the is a problem here. The devices makes acoustic echos, my devices microphone takes voice from speaker and send it back to user. there is 4 cm distance between microphone and speaker. I have to solve this problem with using AT commands. AT#SHFEC=1 can not solve this. Can anyone please share experience about this echo problem? If possible i'd be greatful.. Thank you..

**My gsm module is Telit Gl 865 dual v2, and controlling it with PIC microcontroller, using uart for making call, sending message..

 

[BradtheRad]

1.
One tactic you can try is to invert the waveform going to the speakerbox. Then it tends to cancel itself (instead of reinforce) as it comes again round trip through the mic and amplifier.
The signal may already get inverted in your circuitry since it goes through a few amplfiers already. You may need to experiment to see what works best.

2.
Suppose you were to filter out a frequency band in the outgoing audio, so as to minimize the portion which is picked up by the mic?

3.
Or as an alternate method, create an artificial voice waveform which contains frequencies not detected by the mic?

The effect can be improved if you also filter incoming mic signals, to remove the frequency band coming from the speakerbox and amplifying circuitry.