‘Clean Feed’ or ‘Mix-minus’ refers to an output from a studio mixing desk which includes everything that the listener hears except for the equipment you are sending it to.
If somebody is taking part in a programme via a phone or ISDN line, it’s important that they don’t hear their own voice back down the line as this will be delayed. Most radio desks have a clean feed facility built in to the phone or ‘Outside Source’ channel to achieve this.
Likewise with ipDTL, we must not feed the contributor’s voice back to our studio computer, but they still need to hear everything else. Ideally, you’ll have a spare input on an existing outside source channel with associated clean feed. Connect this to the input on your computer sound device.
If you don’t have a spare outside source channel, fear not! You can create your own using an aux or secondary output. Send everything on the desk to the aux output except for the channel which you will be fading up for ipDTL. Now connect the aux output from your mixing desk to the input on your computer.
If you’re really struggling to create a clean feed, just connect a cheap microphone to the input on your computer and use this to communicate with your contributor. Be sure though that your studio monitor speakers are turned off while the contributor is speaking.