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Re: [Discuss-gnuradio] Audio source cannot use 2 outputs (Stereo) in win

From: CEL
Subject: Re: [Discuss-gnuradio] Audio source cannot use 2 outputs (Stereo) in windows
Date: Fri, 3 May 2019 22:24:26 +0000

Hi Gary!

> I have double checked  and  all the windows audio devices I have
> used 
> for the audio source are 2 channels.

I never doubted that – all I wanted to point out that the I think it
was Windows that told the GNU Radio windows audio source it saw only
one channel, and consequently the windows audio source only enabled one
output port.

I was wrong, it turns out! When you look at gr-
audio/liob/windows/windows_source.cc, you'll find the number of output
streams of the block to be hardcoded to be between 1 and 1, so... 1:

                    windows_source::windows_source(int sampling_freq,
                                                   const std::string
                      : sync_block("audio_windows_source",
                                      io_signature::make(0, 0, 0),
                                      io_signature::make(1, 1,

The last line does that.
So, that's a um, underdeveloped feature in the windows audio source.

> They work fine with  WSJT-X, or MAP65.
> The stereo channels I wish to use are the I and Q outputs from my 
> SDRPLay Duo using virtual cables
> (I have tried the speaker outputs from the PC with GNURadio audio
> source 
> and get the same problem)
> Does the audio source work with two channels on linux?

Yes, (haven't tried today, but it /used/ to work), but it sadly shares
nearly no code with the windows audio source. That's due to fact that
Linux' ALSA and Windows' sound API and OS X's Core Audio are pretty

I do have an idea, though, which *might* be a solution to your problem,
but: untested; don't expect wonders.

Has your GNU Radio build portaudio enabled? As said, it's not tested,
but unlike the windows audio source, the portaudio source at least from
the state of the source code (far as I can tell) enables as many
maximum output streams as your card has.
> I am using the latest version of GNURadio on a 64bit win 10
> PC.

Built from source, or where did you happen across it?

> I am really stuck here. Nothing I try allows the second output to be 
> enabled.

Sorry to hear that! We'll try to get you unstuck :)

Best regards,

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