[arm-allstar] DTMF Recognition

[David McGough]

Patrick,

Your results are specific to your system(s). So, I'm commenting about this
so folks don't think this is always the case, because it's not.

If you're picking up "flat" (AKA: discriminator) audio from the FM
receiver which has had no processing at all, then in most cases the PL/DCS
filters in HamVoIP will be needed.

If you're using processed audio (deemphasized) from the radio, many radios 
and repeaters already have adequate filtering.

What's causing DC offset in your audio? If you're seeing DC offset, you
need to check the radio to fob analog interface. Something is wrong there.

Remember that DTMF tones are frequencies between 697Hz and 1633Hz. This 
frequency spread is wide enough that "tone twist" problems can easily 
occur if you don't have all your preemphasis and deemphasis setting 
matched up properly. "Tone twist" simply put is that the audio passband 
response isn't smooth---tones at one end of the passband are louder or 
quieter than tones at the other end. 


73, David KB4FXC


On Sat, 28 Mar 2020, "Patrick Perdue via ARM-allstar" wrote:

> Oh yeah, I can tell you from experience that turning off all the filters 
tends to screw up DTMF recognition. Depending on the node radio, this 
may make it work zero percent of the time. I thought, as one of my node 
radios (baofeng) has a high pass filter anyway, and won't pass CTCSS to 
the network with filters disabled, it would be enough, but I noticed a 
lot of DC offset and other stuff when I tried that, and less reliable 
DTMF recognition.

FWIW, my Motorola Radius SM50, even with the steepest highpass filter on 
HamVoIP, definitely sounds fuller than the Baofeng, but this should 
probably not surprise you much. Flat output with no filtering feeding a 
software highpass rather than a filter stack, etc.
On 3/28/2020 4:52 PM, "Chris Smart via ARM-allstar" wrote:
> Thanks Doug.
>
> So I can't get away with PL and DCS filters off? I like the slightly 
> improved audio doing that, but maybe that's my problem?
>
> At 04:48 PM 3/28/2020, you wrote:
>> Chris,
>>
>> Â Not sure why you are experiencing that but in general DTMF works 
>> fine on
>> most all radios assuming levels and equalization are correct. I use 
>> THF6's,
>> Baofengs, Yaesu mobile, etc and I never have any problems. You said 
>> levels
>> are at 500. That is a starting point and there is no reason it has to 
>> stay
>> there. Set the levels for the radios you are using trying to average
>> between highest and lowest level. All radios are a little different. Use
>> the Asterisk client to observe what is working and what is not. It 
>> displays
>> the decoded character as you key it. Make sure you have the PL or DCS
>> filter turned ON, DCS preferred and that the pre or de-emphasis is 
>> not on
>> if not needed.  Set the levels so that when you speak it peaks to 
>> 6khz or
>> so. The client will give you an idea what digits are not working.
>>
>>
>> *73 Doug*
>>
>> *WA3DSP*
>>
>> *http://www.crompton.com/hamradio <http://www.crompton.com/hamradio>*
>> _______________________________________________
>>
>> ARM-allstar mailing list
>> ARM-allstar at hamvoip.org
>> http://lists.hamvoip.org/cgi-bin/mailman/listinfo/arm-allstar
>>
>> Visit the BBB and RPi2/3/4 web page - http://hamvoip.org
>
> _______________________________________________
>
> ARM-allstar mailing list
> ARM-allstar at hamvoip.org
> http://lists.hamvoip.org/cgi-bin/mailman/listinfo/arm-allstar
>
> Visit the BBB and RPi2/3/4 web page - http://hamvoip.org
_______________________________________________

ARM-allstar mailing list
ARM-allstar at hamvoip.org
http://lists.hamvoip.org/cgi-bin/mailman/listinfo/arm-allstar

Visit the BBB and RPi2/3/4 web page - http://hamvoip.org