Re: [Discuss-gnuradio] Mixing multiple streams to audio

[Marcus Müller]

Hi JOhn,

you mustn't gate=yes in the squelch! The "add" block needs an input sample on every input to generate one sum sample, and thus, every squelch that's currently gating (i.e. not generating any samples) will simply stop the complete flow graph.

The rest looks ok (if you really feed in 15 kHz channels); I'd recommend doing a few things for debugging:

* replace the receiver block with a null source. You should be getting silence. If that doesn't work, post whole flow graph.

* Replace the receiver block with a NBFM transmitter (followed by, if necessary, a "rotator"), so that your generated FM signal ends up in one of the channels, while the rest should see silence.

* Look at the output of the "add" block with a Qt Time sink or so; you might be generating amplitudes that clip in the sound card

* Try 44.1 kS/s instead of 48 kS/s

* observe buffer fillage with the control port perf monitor

Cheers,

Marcus

On 23.05.2017 20:31, John Ackermann N8UR wrote:

Hi --

I'm continuing to work on a multi-channel NBFM receiver using the polyphase filter.  I have the basic system working, but am hung up on how to get audio out of the system; most of my attempts end up either with audio underruns, or stalls that result in overruns.

The relevant portion of the flowgraph is attached.  Each channel ends up at a 15ksps rate and is fed into a power squelch, then a mult block that's used to mute or unmute the audio, then NBFM demod.  The demodulated outputs are at 7.5ksps (though I get the same results with 15ksps) and the seven channels are added.  Then a rational resample to 48ksps, volume control, and audio sink at 48ksps.

I've tried the "gate" param of the power squelch block both off and on, and the "OK to block" option of the audio sink in various combinations, but I'm not able to get clean audio.

I'd appreciate any suggestions.  One thing I wonder about is the placement of the blocks in the stream; would a different order work better?

Thanks for any assistance.

John

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