Back in the good old days, radio and TV talent could be sent out into the field with a link back to the studio and the ability to monitor the station's off-air signal. The fact that they heard their own voices in headphones or ear pieces was not distracting as there was no delay between speaking and hearing. Goodbye analog, hello digital!
With huge delay times resulting from digital broadcast transmitters, you can forget about monitoring off-air. So, today's remote feeds are usually sent through digital codecs and there can be considerable processing time for audio in both directions. Your brain can only handle a relatively short echo of your voice while speaking. As a result, it has become absolutely necessary to keep the remote audio from being sent back to the remote site. This is done with mix-minus: A mix of all needed audio that the remote site needs to hear, minus the audio coming from the remote site itself.
It is usually easy to create one mix-minus feed on a broadcast console. Most consoles have an audition or auxiliary bus which allows the creation of an additional mix of certain console sources without affecting the main or program mix. If a telephone hybrid is fed by this mix, and a codec feed is required later, the console must be reconfigured for each mix-minus. This can create confusion and add complexity to a live broadcast. Also, if the hybrid and codec need to be on-air simultaneously, a single mix-minus is insufficient. Newer consoles may provide for more than one mix-minus feed but you always seem to need one more!
With the Mix-Minus Bridge (MMB), you can easily create up to six dedicated mix-minus feeds with each remote source having its own dedicated, full-time feed. No configuration is necessary before airing single or multiple remote sources. The MMB simply requires that you configure an audition or auxiliary bus on your console with a single mix-minus but it will remain permanently configured. There is also an interruptible fold back input (IFB) for sending producer cues to the field.
Additionally, the MMB can be expanded to 12, 18 or more channels by stacking units interconnected by CAT5 cables.