DTMF Decode

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DTMF Decode

Ken Walker-3
Hello list,

     I have a new SVXLINK setup I just brought up. It is having problems
decoding DTMF tones. When I run Dtmf_Plot I see an acceptable level for the
tones (about 92%) and every tone is decoded properly with each key press.
However, when svxlink itself is running, I only get the 1,4,5,7,8,0,* & # keys
to decode.

     I am running this setup using discriminator audio into the sound card and
have demphasis enabled in the config file. Is it possible the demphasis routine
is mucking up the decoding of the tones? Does the dtmf_plot program look at and
honor that config variable?

Thanks,
Ken


--
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Re: DTMF Decode

Tobias Blomberg
On Monday 14 August 2006 19:57, Ken Walker wrote:

> Hello list,
>
>      I have a new SVXLINK setup I just brought up. It is having problems
> decoding DTMF tones. When I run Dtmf_Plot I see an acceptable level for the
> tones (about 92%) and every tone is decoded properly with each key press.
> However, when svxlink itself is running, I only get the 1,4,5,7,8,0,* & #
> keys to decode.
>
>      I am running this setup using discriminator audio into the sound card
> and have demphasis enabled in the config file. Is it possible the demphasis
> routine is mucking up the decoding of the tones? Does the dtmf_plot program
> look at and honor that config variable?

Dtmf_plot is not reading the configuration file at all. It was not supposed to
be released at all. It was a tool I used during development. However, it
turned out to be quite useful after all so I released it. I have thought of
developing a new application to help adjusting audio settings. The need for
such an application have increased after adding the audio processing (like
deemphasis) to SvxLink.

The deemphasis certainly is your problem. You can verify this by temporarily
turning it off in the configuration file. All audio processing code is very
experimental and will probably have some unexpected effects.

Please try to adjust the input gain up or down (most likely down) to get
better DTMF decoding. I'm afraid you have limited use for dtmf_plot when
using the deemphasis filter.

I usually adjust the input gain with open squelch so that the noise ends up
peaking just above 90% on the peak meter in dtmf_plot. The DTMF tones peak a
lot lower at maybe 50-60%. This could be a good adjustment to start with. If
you set the gain to high you risk having the signal distorted even before
SvxLink start to process the audio. This is not a good point to start at. I'm
planning to add an AGC at the front of the audio processing chain and maybe
an adjustable gain stage at the end of the chain. These tools can be used to
get the right audio levels in the end instead of overdriving the sound card
input.

If you feel like experimenting a bit, find the file svxlink/rx/LocalRx.cpp. In
there, find the line "deemph_filt->setOutputGain(4);" and try to adjust the
gain value up or down to make it work. Recompile it all and try it. Do this
after adjusting the audio level as described above.

Please report to the list what you did to make it work if you get it to work.

73 de SM0SVX / Tobias

>
> Thanks,
> Ken
>
>
> --
> Unix IS user friendly...It's just choosy about who it calls friend!
>
>
> -------------------------------------------------------------------------
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Re: DTMF Decode

Ken Walker-3
Quoting Tobias Blomberg <[hidden email]>:

> On Monday 14 August 2006 19:57, Ken Walker wrote:
> > Hello list,
> >
> >      I have a new SVXLINK setup I just brought up. It is having problems
> > decoding DTMF tones. When I run Dtmf_Plot I see an acceptable level for the
> > tones (about 92%) and every tone is decoded properly with each key press.
> > However, when svxlink itself is running, I only get the 1,4,5,7,8,0,* & #
> > keys to decode.
> >
> >      I am running this setup using discriminator audio into the sound card
> > and have demphasis enabled in the config file. Is it possible the demphasis
> > routine is mucking up the decoding of the tones? Does the dtmf_plot program
> > look at and honor that config variable?
>
> Dtmf_plot is not reading the configuration file at all. It was not supposed
> to
> be released at all. It was a tool I used during development. However, it
> turned out to be quite useful after all so I released it. I have thought of
> developing a new application to help adjusting audio settings. The need for
> such an application have increased after adding the audio processing (like
> deemphasis) to SvxLink.
>
> The deemphasis certainly is your problem. You can verify this by temporarily
> turning it off in the configuration file. All audio processing code is very
> experimental and will probably have some unexpected effects.

If I disable deemphasis, the DTMF tones decode properly.

> Please try to adjust the input gain up or down (most likely down) to get
> better DTMF decoding. I'm afraid you have limited use for dtmf_plot when
> using the deemphasis filter.
>
> I usually adjust the input gain with open squelch so that the noise ends up
> peaking just above 90% on the peak meter in dtmf_plot. The DTMF tones peak a
> lot lower at maybe 50-60%. This could be a good adjustment to start with. If
> you set the gain to high you risk having the signal distorted even before
> SvxLink start to process the audio. This is not a good point to start at. I'm
> planning to add an AGC at the front of the audio processing chain and maybe
> an adjustable gain stage at the end of the chain. These tools can be used to
> get the right audio levels in the end instead of overdriving the sound card
> input.

OK, I adjusted the mixer input to get the DTMF tones at about 55% and the open
squelch (well with discriminator audio there really is no squelch (*: ) about
88% With the deemphasis enabled, I didn't see any changes in the keys it could
decode. (see below)

>
> If you feel like experimenting a bit, find the file svxlink/rx/LocalRx.cpp.
> In
> there, find the line "deemph_filt->setOutputGain(4);" and try to adjust the
> gain value up or down to make it work. Recompile it all and try it. Do this
> after adjusting the audio level as described above.

I tried with values from 1 to 8. 1&2 almost all tones wouldn't decode. 3-5 same
tones decoded as above. I am never able to get A-D tones to decode. 6-8 only
tones in the first row decoded 1,4,7,*.

>
> Please report to the list what you did to make it work if you get it to work.

reporitng as ordered sir!

The only real reason to use discriminator audio in this case was i was trying to
use CTCSS tone decoding to open the squelch, which is working (tone of 127.3).
All other audio points after the deemphasis circuit also include a HPF that
cuts off all energy below 300 HZ.

Ken - KC9GKA
>
> 73 de SM0SVX / Tobias


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Re: DTMF Decode

Tobias Blomberg
On Monday 14 August 2006 22:41, Ken Walker wrote:
> Quoting Tobias Blomberg <[hidden email]>:
> > The deemphasis certainly is your problem. You can verify this by
> > temporarily turning it off in the configuration file. All audio
> > processing code is very experimental and will probably have some
> > unexpected effects.
>
> If I disable deemphasis, the DTMF tones decode properly.

As expected since it worked in dtmf_plot.

>
> > Please try to adjust the input gain up or down (most likely down) to get
> > better DTMF decoding. I'm afraid you have limited use for dtmf_plot when
> > using the deemphasis filter.
> >
> > I usually adjust the input gain with open squelch so that the noise ends
> > up peaking just above 90% on the peak meter in dtmf_plot. The DTMF tones
> > peak a lot lower at maybe 50-60%. This could be a good adjustment to
> > start with. If you set the gain to high you risk having the signal
> > distorted even before SvxLink start to process the audio. This is not a
> > good point to start at. I'm planning to add an AGC at the front of the
> > audio processing chain and maybe an adjustable gain stage at the end of
> > the chain. These tools can be used to get the right audio levels in the
> > end instead of overdriving the sound card input.
>
> OK, I adjusted the mixer input to get the DTMF tones at about 55% and the
> open squelch (well with discriminator audio there really is no squelch (*:
> ) about 88% With the deemphasis enabled, I didn't see any changes in the
> keys it could decode. (see below)
>
> > If you feel like experimenting a bit, find the file
> > svxlink/rx/LocalRx.cpp. In
> > there, find the line "deemph_filt->setOutputGain(4);" and try to adjust
> > the gain value up or down to make it work. Recompile it all and try it.
> > Do this after adjusting the audio level as described above.
>
> I tried with values from 1 to 8. 1&2 almost all tones wouldn't decode. 3-5
> same tones decoded as above. I am never able to get A-D tones to decode.
> 6-8 only tones in the first row decoded 1,4,7,*.

Ok, thanks for that test. The deemphasis filter does not seem to work so good.
The decoding should work better with than without the filter. I'll have to
work on this code some more.


> > Please report to the list what you did to make it work if you get it to
> > work.
>
> reporitng as ordered sir!

Hmmm... I guess my English is influenced by Hollywood ;-)


>
> The only real reason to use discriminator audio in this case was i was
> trying to use CTCSS tone decoding to open the squelch, which is working
> (tone of 127.3). All other audio points after the deemphasis circuit also
> include a HPF that cuts off all energy below 300 HZ.

Ok, have you actually tried to use the audio after the HPF?  Some RX:s let
through enough audio below 300Hz to make the CTCSS detector work anyway. If
it doesn't work, try to use a tone with a higher frequency if possible.

Another thing you could try is to build yourself an external deemphasis
filter. I've never done this but I think it's quite simple. If I've not
misunderstood the deemphasis process completely, a simple low pass filter
should be sufficient. I'm not sure about the cutoff frequency but in my
digital filter I use 300 Hz.

73 de SM0SVX / Tobias

>
> Ken - KC9GKA
>
> > 73 de SM0SVX / Tobias
>
> -------------------------------------------------------------------------
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> [hidden email]
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Re: DTMF Decode

Ken Walker-3
In reply to this post by Tobias Blomberg
Tobias,
     Just an update on this issue. I finally got some time to look at this again
and found out the tones weren't be accepted because they were falling outside
the MIN_TWIST limit using discriminator audio with deemphasis enabled.

     You had this set at -8, and some of my tones were coming in at up to -13. I
readjusted to -15 and all decode fine now.

Ken - KC9GKA

Quoting Tobias Blomberg <[hidden email]>:

> On Monday 14 August 2006 19:57, Ken Walker wrote:
> > Hello list,
> >
> >      I have a new SVXLINK setup I just brought up. It is having problems
> > decoding DTMF tones. When I run Dtmf_Plot I see an acceptable level for the
> > tones (about 92%) and every tone is decoded properly with each key press.
> > However, when svxlink itself is running, I only get the 1,4,5,7,8,0,* & #
> > keys to decode.
> >
> >      I am running this setup using discriminator audio into the sound card
> > and have demphasis enabled in the config file. Is it possible the demphasis
> > routine is mucking up the decoding of the tones? Does the dtmf_plot program
> > look at and honor that config variable?
>
> Dtmf_plot is not reading the configuration file at all. It was not supposed
> to
> be released at all. It was a tool I used during development. However, it
> turned out to be quite useful after all so I released it. I have thought of
> developing a new application to help adjusting audio settings. The need for
> such an application have increased after adding the audio processing (like
> deemphasis) to SvxLink.
>
> The deemphasis certainly is your problem. You can verify this by temporarily
> turning it off in the configuration file. All audio processing code is very
> experimental and will probably have some unexpected effects.
>
> Please try to adjust the input gain up or down (most likely down) to get
> better DTMF decoding. I'm afraid you have limited use for dtmf_plot when
> using the deemphasis filter.
>
> I usually adjust the input gain with open squelch so that the noise ends up
> peaking just above 90% on the peak meter in dtmf_plot. The DTMF tones peak a
> lot lower at maybe 50-60%. This could be a good adjustment to start with. If
> you set the gain to high you risk having the signal distorted even before
> SvxLink start to process the audio. This is not a good point to start at. I'm
> planning to add an AGC at the front of the audio processing chain and maybe
> an adjustable gain stage at the end of the chain. These tools can be used to
> get the right audio levels in the end instead of overdriving the sound card
> input.
>
> If you feel like experimenting a bit, find the file svxlink/rx/LocalRx.cpp.
> In
> there, find the line "deemph_filt->setOutputGain(4);" and try to adjust the
> gain value up or down to make it work. Recompile it all and try it. Do this
> after adjusting the audio level as described above.
>
> Please report to the list what you did to make it work if you get it to work.
>
> 73 de SM0SVX / Tobias

--
Unix IS user friendly...It's just choosy about who it calls friend!


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Re: DTMF Decode

Tobias Blomberg
Hi Ken!

Sorry, forgot to answer this e-mail.

On Wednesday 25 October 2006 22:41, Ken Walker wrote:
> Tobias,
>      Just an update on this issue. I finally got some time to look at this
> again and found out the tones weren't be accepted because they were falling
> outside the MIN_TWIST limit using discriminator audio with deemphasis
> enabled.
>
>      You had this set at -8, and some of my tones were coming in at up to
> -13. I readjusted to -15 and all decode fine now.

Thanks for the feed back. I have to check what the deemphasis filter is
actually doing. It doesn't seem to be completely ok.

73 de SM0SVX / Tobias

>
> Ken - KC9GKA
>
> Quoting Tobias Blomberg <[hidden email]>:
> > On Monday 14 August 2006 19:57, Ken Walker wrote:
> > > Hello list,
> > >
> > >      I have a new SVXLINK setup I just brought up. It is having
> > > problems decoding DTMF tones. When I run Dtmf_Plot I see an acceptable
> > > level for the tones (about 92%) and every tone is decoded properly with
> > > each key press. However, when svxlink itself is running, I only get the
> > > 1,4,5,7,8,0,* & # keys to decode.
> > >
> > >      I am running this setup using discriminator audio into the sound
> > > card and have demphasis enabled in the config file. Is it possible the
> > > demphasis routine is mucking up the decoding of the tones? Does the
> > > dtmf_plot program look at and honor that config variable?
> >
> > Dtmf_plot is not reading the configuration file at all. It was not
> > supposed to
> > be released at all. It was a tool I used during development. However, it
> > turned out to be quite useful after all so I released it. I have thought
> > of developing a new application to help adjusting audio settings. The
> > need for such an application have increased after adding the audio
> > processing (like deemphasis) to SvxLink.
> >
> > The deemphasis certainly is your problem. You can verify this by
> > temporarily turning it off in the configuration file. All audio
> > processing code is very experimental and will probably have some
> > unexpected effects.
> >
> > Please try to adjust the input gain up or down (most likely down) to get
> > better DTMF decoding. I'm afraid you have limited use for dtmf_plot when
> > using the deemphasis filter.
> >
> > I usually adjust the input gain with open squelch so that the noise ends
> > up peaking just above 90% on the peak meter in dtmf_plot. The DTMF tones
> > peak a lot lower at maybe 50-60%. This could be a good adjustment to
> > start with. If you set the gain to high you risk having the signal
> > distorted even before SvxLink start to process the audio. This is not a
> > good point to start at. I'm planning to add an AGC at the front of the
> > audio processing chain and maybe an adjustable gain stage at the end of
> > the chain. These tools can be used to get the right audio levels in the
> > end instead of overdriving the sound card input.
> >
> > If you feel like experimenting a bit, find the file
> > svxlink/rx/LocalRx.cpp. In
> > there, find the line "deemph_filt->setOutputGain(4);" and try to adjust
> > the gain value up or down to make it work. Recompile it all and try it.
> > Do this after adjusting the audio level as described above.
> >
> > Please report to the list what you did to make it work if you get it to
> > work.
> >
> > 73 de SM0SVX / Tobias
>
> --
> Unix IS user friendly...It's just choosy about who it calls friend!
>
>
> -------------------------------------------------------------------------
> Using Tomcat but need to do more? Need to support web services, security?
> Get stuff done quickly with pre-integrated technology to make your job
> easier Download IBM WebSphere Application Server v.1.0.1 based on Apache
> Geronimo
> http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642
> _______________________________________________
> Svxlink-devel mailing list
> [hidden email]
> https://lists.sourceforge.net/lists/listinfo/svxlink-devel

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