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I'm trying to set GNU Radio as an audio processor for a little community radio in my town.

I've already installed GNU Radio and it's working, but I'm not a sound engineer, so I need some help.

This is my installation:

MIC & Music Player ----> Mixer ----> GNU Radio ---> FM Emitter

I need to know what filters and modules to set to improve sound in this workflow.

Could any of you give me an outline of what GNU Radio modules to use?

Marcus Müller
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JuanMatias
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  • Is this actually about programming? It sounds more like configuring an existing program, in which case it probably belongs on SuperUser. – Jerry Coffin Apr 29 '15 at 01:03
  • @jerry, I don't know, I came here since in GNURadio site it is suggested to ask here. Should I close this question before open it again in SuperUser? – JuanMatias Apr 29 '15 at 01:54
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    It sounds like you what you want is *audio* processing. GNU Radio is primarily a *software-defined radio* platform, implementing actual modulators and demodulators in software. Signals are signals and GR can be used to work with audio signals, of course, but I doubt it'll be the easiest tool for the job; you'd be better off getting something meant for audio processing. In any case, this question is too broad; you'd have to at least describe what kind of processing you want to do to the audio. What will sound better is either subjective or depends on what specific problem you have. – Kevin Reid Apr 29 '15 at 03:50
  • @KevinReid, we have issues with output sound levels and stability. So I think we need at least a compressor, a normalizer and an equalizer. We want to improve sound and make output signal stable. – JuanMatias Apr 30 '15 at 02:35
  • @JuanMatias OK, so you _could_ do those using GNU Radio (AGC and filter blocks), but I still think you should look at dedicated audio processing software instead. – Kevin Reid Apr 30 '15 at 04:10
  • @KevinReid, you're right. I think I can do this with Jack and a couple of Jack's tools. I need more research but you've put me on the right track, thanks! – JuanMatias May 01 '15 at 04:32

2 Answers2

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Since the aim is to improve sound quality in our little community radio, the right way to achieve it is to use an audio processor software, as @KevinReid said.

For the records, one possible solution is use this schema with Jack:

MIC & Music Player ----> Mixer ----> PC with audio processor ---> FM Emiter

The PC with audio processor is a GNU/Linux based PC with Jack as sound server and Calf Jack Hub (calf.sourceforge.net) as audio processor.

Steps:

  1. Install jack, qjackctl and calf.
  2. Open qjackctl and start jacks server
  3. Open calf and set filters you want (eq, limiter, compressor, etc.)
  4. Set connections so you take the input, send it through filters, put it into the output (i.e. headset connector or lineout)

That's all. All this can be done by command line, at startup, etc... but this shows the main idea.

JuanMatias
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You can simply use alsa or pulse audio to configure a "virtual" capture device, use that as the device name in the GNU Radio audio sink, FM modulate the audio signal and send the result to your RF hardware. That's pretty much a typical GNU Radio use case. You might want to have a look at the gr-analog examples :)

Marcus Müller
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