DTMF inbound and Digital Receptionist

[leejor]

I have had to increase it up to +6, which I believe is quite high and haven't tested yet what effects has over the rest of the communication.
I am going to try to change also impedance in the port, which might affect the quality...

You can increase the gain but do run the risk callers getting echo. If they don't complain, then leave it at the point where it solves your problem. Changing the impedance can have detrimental effects on call quality and also introduce echo, but, once again, if changes don't cause those issues, then there is no harm in changing if it solves your problem. The defaults, for the 3102. are the best under ideal situations in the North American telecom market.

 

[SY]

To be honest I don't understand what is +6 in SPA3102 configuration.
+6 of what?
+6 to what?

Is there any description of this parameter available?
Why does it cause the echo?
What is the reason of that echo?

 

[aznarepse]

According to the Admin manual of the SPA:
"dB of digital gain (or attenuation if negative) to be applied to the signal sent from the PSTN side to the SPA. The range is -15 to 12. The default is 0."

My new value is +7.

It could be that provokes some echo, but it is more likely to be produced by a mismatched impedance in the FXO port.
I have taken a new wireshark and all the DTMF tones are parsed Out-of-Band now, no matter if I transmit them from the memory or when the DR is talking or not.

I am trying to get more wireshark with some voice to be able to assess the quality of the call, but it is a bit difficult now for me, for I am working remotely with my server with a very slow internet connection. Nevertheless, I have been able to make a call and talk normally.

Thank you very much to everybody who has helped me out!

 

[SY]

"Db" is relative (and logarithmic) value. What is the basis? What is the definition of "0 Db"?

 

[abc123]

"Db" is relative (and logarithmic) value. What is the basis? What is the definition of "0 Db"?

the basis is based on the amplitude of the incoming analog waveform.

It you attenuate by 3db you will halve the amplitude and hence the volume, because as you say it is logarithmic.

It is not a scale based on a single point (such as degrees Celsius or Kelvin) but is a relative scale as it is amplification (or attenuation in the negative of whatever it is given.

So the +7 in the OP's 3102 means it is amplifying whatever it receives by 7db (which is a lot!).

 

[leejor]

"Db" is relative (and logarithmic) value. What is the basis? What is the definition of "0 Db"?

I would imagine that is something that would have to be put to the people at Linksys/Cisco. Perhaps, when set at "0" a tone (1Khz?) sent from the PSTN, via VoIP, to an ATA, to a phone, comes out at the same level. When tones are sent in the telephone industry, it is just the impedance that can vary, a tone generator set to 0 db is assumed to be 0 db in all tests performed. "0 dBV Preferred informal abbreviation for the official dB (1.0V); a voltage reference point equal to 1.0 Vrms."

The problem with boosting levels too much is when that higher volume hits the hybrid in an analogue telephone, some of that audio will feed back to the caller. If there is enough of a delay (long distance calls), then it means echo to the caller. It probably won't be as much of an issue with a digital set as the send and receive path can remain separate.

 

[SY]

"Db" is relative (and logarithmic) value. What is the basis? What is the definition of "0 Db"?

the basis is based on the amplitude of the incoming analog waveform.

It you attenuate by 3db you will halve the amplitude and hence the volume, because as you say it is logarithmic.

It is not a scale based on a single point (such as degrees Celsius or Kelvin) but is a relative scale as it is amplification (or attenuation in the negative of whatever it is given.

So the +7 in the OP's 3102 means it is amplifying whatever it receives by 7db (which is a lot!).

+7 Db is very significant amplification. It is not a question.

Sorry, I didn't formulate my questions clearly .
the questions are:
How is this setting used by SPA3102?
Does SPA3102 amplifies analogue signal before passing it to ADC or it amplifies digital signal received from ADC? on which level it recognizes DTMF signals?
Why only +7 Db passes threshold of the recognition reliability?
Why SPA3102 cannot recognize DTMF signals which are recognized by PBX(IVR)?
Why SPA3102 recognizes DTMFs (converts it to out-of-band) only in case if they are received at the time when audio signal from IVR is significant and stops to do it right after IVR sends very low audio signal?

All questions are based on the review of wireshark capture.

Thanks

P.S. "Db" is also applied to different chracteristics. Sometimes +3 applied to one of them is equal to +6 applied to the other...

 

[abc123]

The answer to your question is "does anyone including themselves know how linksys/cisco work?"

 

[aznarepse]

Hi,
I don't know how exactly the SPA3012 manages the input and the gateway flow. Considering the possible settings, "SPA to PSTN gain" and "PSTN to SPA gain", I reckon that it amplifies or attenuates the original signal at the input, before it is processed.
I have reached the value +7 by trial and error. I started with the default and tested until all the tones are parsed to Out-of-band (most of the times). Indeed, the question is why the SPA is parsing the tones and not delivering them transparently.
As I said, I am away from home and cannot really manage big files over the crap network and VPN I am working with. But, I have been using the phone and have asked people about the quality of my signal after the change and everybody says it is good (I call my home and the 3CX transfer my call to the number I wish; my call is amplified while passing the SPA3012). Again, all this is quite new set up I have and I can say that the signal I had on the PSTN line was very weak; I always had to speak quite loud on the phone and it was hard to hear as well. The first thing I did when I installed the SPA was to increase the gain in the port of the handset but I actually didn't think about the FXS port.
Once again, thank you very much for your help!

All the best,
Adan
PS if someone wants to have a look at a wireshark with +7 and all the tones parsed I have one and will email...

 

[SY]

It will be interesting to look on wireshark capture of the same call(access to voice mail box) but in case of +7 Db amplification.
You know my e-mail

Thanks

 

[leejor]

I can say that the signal I had on the PSTN line was very weak; I always had to speak quite loud on the phone and it was hard to hear as well.

You should not have to compensate for an overly attenuated phone line. Unless you are out in the middle of nowhere you should be complaining to your phone company about poor service/low level. There may be a bad cable, faulty line equipment or other reason, that can be fixed, to blame.