Virtual Audio connectivity

Unless the radio is used directly at the desk, with a set of speakers plugged into it, it’s not possible to hear any audio output. Equally to use the output in Fldigi to decode CW, PSK31 etc there needs to be a mechanism to pipe the audio between applications.

A virtual audio program pipes the output from SDRConsole, normally destined for your speakers, onto an audio bus which is then available to any application requiring an audio input. As many applications as are necessary can tap into this bus and multiple virtual cables can be created.

Sounds complicated? Trust me it isn’t when you’ve got the very simple setup and config screens in front of you.

Think of a virtual audio cable as any other lead that you plug things into or equally plug into things. The only difference is it isn’t physical.

Screenshot 2014-11-26 12.05.01   Screenshot 2014-11-26 12.05.31

 

As the screen shots show, once installed on a system, Windows displays the Virtual Cable as any other sound device plugged into the machine.

There are several virtual audio packages in existence which attempt, with varying degrees of success, to achieve this.

 

The most popular is Virtual Audio Cable (current version is 4.14)

vacsetup-4

http://software.muzychenko.net/eng/vac.htm

 

A free alternative is VB-Audio Virtual Cable

R5QYQ

http://vb-audio.pagesperso-orange.fr/Cable/index.htm

Unfortunately as hard as I tried I just couldn’t get VB-Audio Virtual Cable to work, which is a shame as it looks good.

 

Virtual Audio Cable on the other hand worked instantly. To get the audio out of SDRConsole and into Fldigi it’s as simple as selecting the Audio setting within SDConsole

Audio -> playback -> Line 1 (VAC)

Fldigi is using the virtual audio as an input source and everything, just works.

VAC has its own control panel and I’ve left it purely as the default settings.

 

To get a feel of how it works and to satisfy my curiosity, following this section of the manual gave great proof of concept, especially when you run the Audio Repeater. There are two available to select from and I used the MME one.

Simple cable usage

To use a cable simplest possible way, first run VAC Control Panel application and make sure that there are 1-3 cables and they are configured with typical parameters:

  • Maximum instances – 20
  • Milliseconds per interrupt – 5..7
  • Sampling rate range – 22050..48000
  • Bits per sample range – 8..16
  • Number of channels range – 1..2
  • Stream format limiting – Cable range
  • Volume control – disabled
  • Channel mixing – enabled
  • PortCls usage – disabled

Don’t close VAC Control Panel, it will help you later.

Run any audio producing application (a player, a tone generator, an audio editor) that allows you to specify a playback/render device directly and choose Virtual Cable 1.

Start playback and make sure that the application really plays to Virtual Cable 1. You should hear nothing but VAC Control Panel must show 1 or 2 new playback streams for Virtual Cable 1 and cable signal level indicator should be shown. If you hear a played sound, it means the application directs it to your hardware audio device, not to Virtual Cable 1.

If a sound is really played to the Virtual Cable 1, run Audio Repeater (MME variant) application and choose Virtual Cable 1 as a recording (Wave In) device and your hardware audio device as a playback (Wave Out) device.

Activate audio transfer clicking Start button in Audio Repeater. Now you must hear a sound played by an application started first and the Control Panel application must show a new recording/capture stream. It means that audio data are transferred from a playing application to Virtual Cable 1 and then Audio Repeater transfers them further to a hardware audio device. You have created a full audio path containing Virtual Cable 1.

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