if two programs access sound cards and you want to connect them, you need a virtual sound cable. The best example of this is the connection of the SDR console with other programs (HSmodem, SSTV, RTTY …)

The SDR console delivers the received and demodulated NF signal to a sound card, where you can e.g. connect to a loudspeaker .

HSmodem expects the NF signal from the microphone input of a sound card.

How do you connect the output of the SDR console to the input of the HSmodem? This is done with the help of a virtual sound cable (VAC). A VAC couples an audio output with an audio input. If you not only want to receive but also to send, you need a separate VAC for each direction.

This is only about Windows (of course there is something like that for Linux too):

Receiving way: SDR (e.g. Pluto) → SDR console → VAC → HSmodem → monitor

We tested the virtual sound cable from vac.muzychenko.net, which works well, it can be purchased from Autor for little money.

Another VAC is available from vb-audio.com. In the simplest version, this also offers only one channel, but can be expanded to a higher version through a donation (donationware).

The free versions of the various providers only ever have one audio channel. Since we need two channels for sending and receiving, either the commercial version or two free versions from different manufacturers are used.

There are certainly other providers, but they have not been tested in this context.

More information on configuration: see chapter SDR console