Questions regarding APF implementation

W1RE

I see there have been several instances already of people having audio issues due to enabling APF then switching to SSB where apparently the APF is still active and causing confusion as to why the audio "is not working correctly".

Is there even a reason for APF to be active in a that's not in CW mode?  Why would SmartSDR bypass APF if not appropriate?

Today APF is a radio-wide CW Transmitter Control setting affecting all slices.  Should it maybe be on a slice-by-slice basis or at least bypassed when not appropriate for the mode?

 - Bob, W1RE

Al_NN4ZZ

Bob,
Agree and I think FRS does too.  In the release notes it says  "APF is currently enabled for all modes.  If you have a problem....."  

This implies that they realize it can be an issue and will probably address it in a future release.  I suspect that it will be disabled if the mode is not CW.  

Given the number of problems already reported, and how easy it is to forget to disable it, a fix will probably be in one of the next point releases.

Regards, Al / NN4ZZ

 

Steve-N5AC

There were a lot of requests for APF and we had a very simple method for adding it using the codec in the radio.  All audio output from multiple channels and modes is demodulated, and then combined according to the volume and fade settings in the radio.  The final composite audio is sent to the codec for output to the speakers and/or headphones.  So we implemented this first pass of APF in the codec, but the draw-back is that it affects all output from every mode.  We rationalized that the serious CW guy using this won't have a SSB receiver on at the same time.  But the better implementation is to perform the work before the codec and only on CW slices.  We didn't have time to switch implementations for v1.1, and felt like it was better to get this implementation in your hands with the caveats rather than pull the feature entirely.  We expect the user controls to be the same so there was no danger in getting folks trained on one thing only to switch to another. 

Al_NN4ZZ

Steve,
Sounds good.  Can comment on the questions below also?

 Ken - NM9P, Elmer

My only comment regarding the APF other than THANKS! is wondering if the total gain can be moved down a bit.  It adds SO much gain to the desired signal that I must reduce the headphone volume... Then I must increase my sidetone to compensate.  

If the total gain of APF was reduced a bit, or better, adjustable, then it would make the noise surrounding the signal drop and it would seem that the desired signal would pop out of the noise even more.  But this is just a nit-pic.  

APF is awesome! Thanks for the unexpected but much desired new feature!

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17 hours ago

Al / NN4ZZ

Ken,
Your comments tie in with my questions above and also the idea I submitted a while back that would allow you to control the filter width (relative to the sidetone), peaking gain, and attenuation gain for the frequencies (hiss, noise, etc) outside the filter range.  Maybe that will come at some point.   Anyway what we have is a good improvement.  

Regards, Al / NN4ZZ

Idea is to have a control dedicated to the APF function.  

Al_NN4ZZ

Here are the questions.....

 I couldn't find much in the way of technical information on the APF feature in the user guide.  Did I miss it or if not, can we get some details?   For example: 

1 - The APF is centered on the side tone frequency in the audio chain - how wide is the filter?  5hz, 50hz, etc

2 - How much boost (+db) is provided for the passband?

3 - How much attenuation (-db) is provided for the audio frequencies outside the filter?  There seems to be more noise than I expected.   It would be interesting to check it with a scope. 

Regards, Al / NN4ZZ

Ken - NM9P

Thanks, Steve.  Considering that most of us were not even hoping for APF in this release, I am very happy to have it, even with the initial limitations!

I am sure that it will be given more attention after some other very important enhancements are finished in v. 1.2. 

Thanks for this one.  I have gotten used to its particular quirks and have already found it very useful.  (I wish I would have had it during the most recent 160 test!)

Keep 'em coming, guys.  It's all good stuff.

David Decoons, wo2x

Since APF function is active on all modes it would be a good idea to have an indicator show when it is active in all modes. At least then the user would know it is active.

On SSB the audio is pinched up and hollow when APF is on and there is no visual indication that it is on.

Dave

wo2x

Al_NN4ZZ

Dave,
See this link.  I think it does what you want.   Add your feedback and give it a plus if it does.

https://community.flexradio.com/flexradio/topics/apf_ability_to_control_width_gain_and_attenuation_a...

Regards, Al / NN4ZZ  
al (at) nn4zz (dot) com

Barry N1EU

FWIW, a narrow peaking filter can be quite effective on SSB but it would obviously have to be significantly wider.  I've used a 300hz wide APF and several times it made the difference between reading or not reading a weak ssb signal.