Backgrounddetect help with silence threshold

Good evening!! I have a need here in Brazil, our asterisk systems dial over thousands of lines and play a advertisement trying to induce people to press a touchtone to be transferred to a sales rep. (This is legal in the Brazilian third world / don’t get mad the government down here screws us much harder!). The problem we have is that people hang up on their POTS lines while hearing this message (of course) however in many cases the disconnect/hangup never comes to the calling asterisk systems because the end offices in Brazil date back to the 1960’s and there is no disconnect supervision. So we are trying to use the function backgrounddetect to play the audio and wait for the DTMF however we want to also trigger it to stop if we hear only silence for 10 seconds. This would basically signal to us that there is no one on the other end listening. Does anyone know what the silence threshold setting is for this function. The silence threshold here being the energy level of the noise. We want to set it really low so as to overcome the lack of getting the hangup. Thank you

Another note here is that there seems to be some confusion with the parameter silencethreshold.

In amd.conf there is a parameter called silence_threshold which I have always assumed is the amplitude baseline of silence.

Then in dsp.conf there is a parameter called silencethreshold with no underscore with a definition that conflicts. To me that definition is of duration. And since the calls to waitforsilence allow for setting the silence duration it only makes sense that the silencethreshold parameter in dsp.conf relates to amplitude of sound and not duration. Is there any dsp developer out there that can help us ??
Thank you in advance.