APF - ability to control width, gain and attenuation and mode

Al_NN4ZZ

The new audio peaking filter (APF) feature is good and a big improvement -- here are some ideas to make it better.

- One known issue is that when enabled it applies to all modes.  This causes problems for SSB as noted in the "known issues" list.

- It's been reported by some that It adds SO much gain to the desired signal that you must reduce the headphone volume. If the total gain of APF was reduced a bit, or adjustable, 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.

- The parameters for the filter are not adjustable. In some cases a very narrow filter might be better. Adjustments to the peaking or attenuation of frequencies outside the passband could improve the operation. The APF is centered on the sidetone but other details of the implementation are not provided. It would be helpful to know more about them:

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?

Allowing the user to control these parameters would further enhance this feature. Here is an example of a new APF control panel to illustrate the idea. The control would allow you to adjust the filter width (relative to the sidetone), peaking gain, and attenuation gain for the frequencies (hiss, noise, etc) outside the filter range.

In addition there could be 2 levels for enabling the control if warranted.
-ON / OFF for all digital modes including CW (but not for voice modes)
-ON for CW only

The specific numbers in the example are for illustration. Based on the answers to the 3 questions above other values may be more appropriate.



This idea posting is a composite of previous discussions/comments and ideas for the APF feature before and after the initial implementation in V1.1.  This updated IDEA posting is based on those comments and the operation of the current implementation of the APF in V1.1.  Thanks to Ken/NM9P, Bob/W1RE, Larry/K1UO, Sergey/RA3AJK, Dave/W5UN and others for their input.


Thoughts and comments?

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

Barry N1EU

If you're adding flexibility, why not add the ability to go as wide as 300hz and add ssb mode capability?  With a center frequency of 600-1000hz, such a filter can be quite an effective tool in pulling weak ssb signals out of the noise.