The dxzone.com website has uploaded a post that lists five free virtual audio cable software programs. Virtual audio cable’s allow you to “pipe” or pass the audio from one application to another. For example, in order to pass the audio of a digital P25 signal received in SDR# into a decoding program such as DSD+, you need to use a virtual audio cable. The most commonly recommended software is Virtual Audio Cable, but this software is not free. See the dxzone.com post for their list of five alternatives for Windows, Linux and MaxOS.