engineering

Mix-minus

Mix-minus is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mix-minus rather than just read about it. In short: In audio engineering, a mix-minus or clean feed is a particular setup of a mixing console or matrix mixer, such that an output of the mixer contains everything except a designated input. Mix-minus is often used to prevent echoes or feedback in broadcast or sound reinforcement systems.

Key takeaways

Mix-minus belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mix-minus to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mix-minus from memory before moving on to harder problems.

Reference excerpt

In audio engineering, a mix-minus or clean feed is a particular setup of a mixing console or matrix mixer, such that an output of the mixer contains everything except a designated input. Mix-minus is often used to prevent echoes or feedback in broadcast or sound reinforcement systems.

Examples A common situation in which a mix-minus is used is when a telephone hybrid is connected to a console, usually at a radio station. The person on the telephone hears all relevant feeds, usually an identical mix to that of the master bus, including the DJ's mic feed, except that the caller does not hear their own voice. Mix-minus is also often used together with IFB systems in electronic news gathering (ENG) for television news reporters and interview subjects speaking to a host from a remote outside broadcast (OB) location. Because of the delay that is introduced in most means of transmission (including satellite feeds and audio over IP connections), the remote subject's voice has to be removed from their earpiece. Otherwise, the subject would hear themselves with a slight (but very distracting) delay. Another common example is in the field of sound reinforcement, when people need to hear a full mix except their own microphone. Legislative bodies of government may use a large mix-minus system, for instance houses of parliament or congressional groups that have a small loudspeaker and a microphone at each seat. From the desktop loudspeaker, each person hears every microphone except their own. This enables all participants to hear each other clearly but minimizes problems with acoustic feedback. In 1994, the first digital audio implementation of such a system was installed at the United States Senate building, with more than 100 mix-minus outputs, one for each senator and also guest seats. Mix-minus is also used with VoIP communication when recording for podcasts: mix-minus removes the caller's voice from the VoIP call, but allows them to hear all other channels available at the mixing console (mixer). Some broadcast mixing desks, notably those designed in house by the BBC, maintain a separate mix bus for clean feeds.

References

Illustrations

Worked examples

Example 1 — a first encounter with Mix-minus

Start with the simplest possible case. Write down what Mix-minus claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mix-minus before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mix-minus ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mix-minus

In research: Mix-minus appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mix-minus in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mix-minus is common in secondary-school and first-year university syllabi. It links to neighbouring topics Audio engineering, Broadcast engineering, Satellite broadcasting, so understanding it makes those chapters shorter.
In everyday life: Look for Mix-minus outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mix-minus in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mix-minus means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mix-minus out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mix-minus in simple terms?

Why does Mix-minus matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mix-minus?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mix-minus.