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What Does M/E Mean?

Video Switcher Jargon

So you’re thinking of buying a video switcher, but you don’t know what to buy.

Maybe you’re looking through all the features and you don’t know what all the letters and numbers mean. One big question that commonly arises is: What does M/E mean? What does it do for me? Why do I care?

What does M/E mean?

An M/E (sometimes referred to as an ME or MLE depending on the manufacturer) is a Mix Effect. All the functions that the switcher performs define what that Mix Effect does.

So before we get to the M/E, we should talk about what a M/E isn’t. If you have a punch switch that mechanically selects between sources, and your image on the screen loses sync for a second, that is not a Mix Effect! That would be referred to as a punch switch, bang box, contact closure, pushbutton, bud box, SPST, dead man switch, panic button, etc.

A Mix Effect is used on professional switchers and consists of the following: a crosspoint, a transition area with cuts and a true mix or wipe, a T-Bar, a keyer, and special outputs. Let’s break each of those down.


A crosspoint on a M/E refers to the two rows of buttons that have your video inputs on them. The Crosspoint is usually laid out with one row on top of the other – one row being Program (live on the air) and the other being Preview (what you are previewing to go to air next).

The number of buttons on the crosspoint traditionally is the number of inputs you have on the switcher. So if you have two rows of buttons with eight buttons each, then you probably have an eight-input switcher.

However, this isn’t always true. Due to space constraints, some manufacturers have created ‘Shift’ buttons to allow for more physical inputs to be on the switcher chassis than there are physical buttons. By using the Shift button you are allowed to see twice as many sources on a second bank of shifted inputs.

On switchers with a M/E, the Preview row is always at the bottom, and the Program row is always above it. This allows Technical Directors to comfortably push buttons on the bottom row of an M/E at any time, knowing that they are only affecting the Preview bus.

Transition Area

The transition area is the next aspect of the Mix Effect. Program and Preview are selected by the operator in the crosspoint area and then taken to air by the transition area. The transitions are the ‘Take’ button, which is a cut between Program and Preview. You can use the T-Bar to dissolve between Program and Preview. The ‘Auto-Trans’ button will automatically dissolve between Program and Preview at a pre-defined transition rate.

Beware of imitations! The hallmarks of a true M/E will be a robust T-Bar, not some cheap slider. The T-Bar will dissolve between the Program bus and the Preview bus.

A-B Switchers

There are some switchers out there that allow the T-Bar to dissolve between the top row and the bottom row, and then back again. These are known as A-B switchers. A-B Switchers are not Mix Effects!

In A-B switchers, the Program feed flip-flops between the top row of crosspoints and the bottom row of crosspoints. This means that the Technical Director is constantly pushing buttons on both rows of buttons. When you begin, Program is on the top row (or A-row), then after the flip-flop transition, Program is on the bottom row or B-row. This means that the TD is pushing buttons for Preview on both rows. With A-B switchers there is bound to be an “oops” during your show.

Down Stream Keyer

The next section of the Mix Effect is the downstream keyer section. In the signal path, the keyer occurs after, or ‘down-stream’ of the transition area. The keyer is what allows you to overlay (or superimpose) graphics or video elements on top of the background layer of the video.


There are several different types of keyed effects. A chroma-key replaces one predefined color with video. This is what your local TV station does with the weatherperson. They stand in front of a blue or green screen that is then ‘keyed-out’ and replaced with video; for example a map of your state.

Alpha Key

An alpha key is a special key that requires an alpha channel signal. This requires a device with a special video card that has the ‘fill’ information that you want to put on the screen as well as the ‘alpha’ information that you want to cut out of the screen.

An alpha key is pretty standard with broadcast graphics machines and provides a very clean signal. Even now some off-the-shelf graphics programs are partnering with AJA or BlackMagic video cards and generating alpha information that can then be used by professional switchers to alpha-key.


A linear key, also called a luma-key or self-key, is where the switcher can overlay a graphic image on top of a video without an alpha channel, just by using the difference between the bright and dark information of the graphic. This is where you have a graphic source like PowerPoint that you want to use as your lower-third graphic maker. PowerPoint does not have an alpha channel, so by using a linear key you can create white text on a black background and then the switcher can key out the black background and superimpose the white text on top of the video.

This works relatively well as long as you can control your graphic to do things like drop shadows. Super-fine elements tend to get lost on linear keys.


The final feature of a Mix Effect is outputs. This may sound basic, but low-end switchers do not have the outputs that are required for demanding shows. All legitimate video switchers should have a Program output (the composited video image of the crosspoint with the keyers superimposed), a Preview output (the video image of what is selected on the Preview bus), and a Clean Feed (the Program output, but without any downstream keyers being shown).

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