Way to limit AF?

Buck
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Way to limit AF?

Postby Buck » Thu Jun 15, 2017 3:36 pm

I work a net that covers a large region and whose stations therefore vary widely in volume in my ear. I'm using virtual audio through a Behringer interface. Is there a way to limit the volume? I've tried various combinations of AF and AGC threshold, to no joy. Thanks for any pointers.

Buck
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w-u-2-o
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Re: Way to limit AF?

Postby w-u-2-o » Thu Jun 15, 2017 9:30 pm

Buck,

The use of VAC is no different than the use of the built-in radio sound output in this case, or in any case, really.

The multiplicity of volume controls (RX1 AF, Master AF, VAC RX AF, the volume knob on the Behringer, etc.) might make you think that you can get something for nothing, but ultimately they all just add up to "x" amount of gain.

If you are looking for some sort of automatic volume control or volume control limiter, unfortunately there is no such thing in the radio. However, your RF AGC should be doing a reasonable job of keeping things under control. I'm guessing this is an SSB net? How is your AGC setup for this? I generally use the medium preset with the AGC line set between 3 and 10dB above the displayed average noise level (DANL) on the panadapter, depending on the conditions (good to bad). On very noisy bands 10 or 20dB of attenuation helps. NR2 also helps a lot. I generally leave on all the time, even for signals that are well over S9.

At the end of the day, some amount of manual audio and/or AGC gain riding is necessary.

73,

Scott
N9VX
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Re: Way to limit AF?

Postby N9VX » Thu Jun 15, 2017 11:32 pm

I have had a few Flex and Apache Lab rigs and currently own a ANAN-100B. I talk to a few guys on 160 Meters and one guy is a few blocks away, when he transmits he blows me out and I have to constantly be turning AF/RF gain up and down. I had a Flex 6300 here a while and it does not require me to adjust the AP/RF gain when the guy a few blocks away transmits. I don't know what Flex has done, but I like it!

Joe N9VX
Buck
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Re: Way to limit AF?

Postby Buck » Fri Jun 16, 2017 3:33 am

Thanks, Scott. Yes, we use USB, generally near 60 meters. I use med AGC on the voice side and fast on the digital side. There's already 20 dB set because I have a preamp at the antenna. But there is, naturally, a huge difference between the station in Fountain and one in Montana. Some kind of limiter on AF would be really nice to have. Maybe I will play with Matlab to see if I can model such a thing.

Buck
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w-u-2-o
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Re: Way to limit AF?

Postby w-u-2-o » Fri Jun 16, 2017 12:10 pm

I just had an idea for you, Buck: since you are already using VAC, why not use a DAW (digital audio workstation) application of some sort to implement a compressor/limiter on receive? We always think of doing this for transmit audio, but why not do it for receive, also?

You could use the free evaluation version of AudioMulch to see if you can get something to work. There is also Ardour a sort of free, open source DAW, but it is much more complex than AudioMulch. There are lots of goodYoutube videos on how to setup AudioMulch.

I have a somewhat dated paper here on how to jack a DAW into Voicemeeter to do things like that. It's not a cookie cutter, step by step, answer, but it should provide enough guidance for you to figure it out.

73,

Scott
Buck
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Re: Way to limit AF?

Postby Buck » Mon Jul 10, 2017 3:33 pm

Scott, I recently got access to MATLAB, and it has a Simulink block that implements a volume limiter. I set it up with this chain: VAC1>Windows Direct Sound> Muzychenko's VAC>Simulink Model>Windows Direct Sound>UMC202HD>Headphones and Speakers. The model applies up to 40dB attenuation. I was also able to compile the model to run in a terminal window, using the same audio chain, and can swap it out by redirecting VAC1 to the UMC's ASIO.

It actually works pretty well, though it adds latency and some popping because of the extended audio chain. Something like this might be a good candidate for the VAC setup page, perhaps with a slider to set the amount of attenuation.

Buck ko0y
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w-u-2-o
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Re: Way to limit AF?

Postby w-u-2-o » Mon Jul 10, 2017 4:58 pm

Hi Buck,

If this is a problem for VAC, it's also a problem for the radio speaker/headphone output. The feed (from RX1, anyway) is the same.

It is interesting that you used MATLAB. To me that seems like an unnecessary level of complexity, but then again I am very comfortable with DAW software and perhaps you are very comfortable with MATLAB.

However, if you want to get rid of the clicks and pops, you might try using a compressor/limiter in a DAW, like Audiomulch, as a DAW is expressly designed to process real-time audio smoothly.

As far as I know, you are the only person who has shown an interest in a dedicated audio AGC function.

73,

Scott
Jay_N2MGA
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Re: Way to limit AF?

Postby Jay_N2MGA » Tue Aug 15, 2017 3:33 am

Hello Buck and everyone, I ran into this same scenario, loud/strong USB signals in a group mixed with weak/softer ones, using headphones became a problem for me with the loud/strong stations boosting the audio & AGC Gain to hear the weaker ones. I found some success using the AGC Slope setting located in the Setup/DSP/AGC-ALC screen, look for the RX1 or RX2 Slope setting located right above the AGC Max Gain box. Try at least 3db Slope or more to even out the audio between the strong stations and the weak ones. I typically use around 6db adjusting as needed. Works very well for SSB.

hope this helps...

'73
jay
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w-u-2-o
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Re: Way to limit AF?

Postby w-u-2-o » Tue Aug 15, 2017 11:27 am

Great suggestion, Jay! :)

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