‘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 podcast, interview or radio 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 (sound boards) have a clean feed facility built in to the phone or ‘Outside Source’ channel to achieve this.
Likewise with ipDTL or sip.audio 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.