Communications156 APOLLO Digital Broadcast Production ConsoleMIX MINUSMix Minus is a system that allowsa comprehensive mix to be sent tomultiple listeners each receiving thecomplete mix, minus their own input.Fig 1 shows an abstraction exampleof a mix minus system. Assume thatthe sources surrounded by a blue boxrepresent people, either presenters orfield reporters. The other sources mayrepresent VT or server audio feeds.These sources are fed to the input of eightchannels on a console. Each channel hasthe option for its signal to be sent to theconsole wide mix minus bus.This mix minus bus can be routed backout to any sources that may requirefoldback, for example the presenters orfield reporters. Each source would befed the entire mix-minus bus signal, withtheir own contribution to that mix removed,creating an unique feed.In Fig 1 the mix sent back to source 1would consist of sources 2-8, source 2would receive a mix of sources 1 and 3-8and so on...Why remove a source’s input fromits foldback mix?Two reasons are presented here. The firstrelates to field reporters, or presenters instudios communicating via long distancesystems such as satellite links.The reporter would need to hear a mix ofthe show’s audio in order to hear cues andcommunicate with the presenters. Theinherent delay in these systems meansthat it may be a number of seconds beforethe audio reaches the reporter.It can be very difficult to speak whilehearing your own voice returned to youwith even a slight delay. By using a mixminus feed to the reporter, their owncontribution to the audio is removedbefore it is fed back to them eliminatingthis problem.The second reason is to eliminatefeedback. If a presenter’s foldback wasmonitored on loudspeakers withoutsubtracting their own contribution, someof their original signal may be picked upby the microphone again, thus creatinga feedback loop. By using a mix minussystem to remove the presenter’s owncontribution, this feedback loop is broken.Sending signals to the mix minusbusThere is one mono mix minus bus, which isa global bus that any path can contributeto.FIG 1 - MIX MINUS ABSTRACTIONMixMinusBusInputfromsource 1Feed tosource 1minusInputfromsource 2Inputfromsource 3Inputfromsource 4Inputfromsource 6Inputfromsource 7Inputfromsource 8Feed tosource 6minusFeed tosource 8minusFeed tosource 2minusFeed tosource 3minusInputfromsource 5
