Vision mixer

A vision mixer (also called trick mixer ) is a device that is used to switch between different video sources to mix these or sometimes also add special effects, similar to a mixer for clay used. A video mixer is typically found in a television studio, a television broadcast van or on a linear editing suite. The term " vision mixer " can also refer to the person operating the device.

Skills and use

Besides hard cuts ( switching directly between two image sources), an image mixer also a number of transitions ( Transitions) create, from simple transitions (Mix or dissolve ) to wipe ( Wipe ). In addition, most mixers punching (Keys) can display and generate color signals ( in this context, mostly as " Matt " means ). Most vision mixers are designed for professional use, so have the older analog models component connections and modern digital models SDI connections. They are used for live broadcasts, recordings on video cassettes and for the linear section. On average, the area they have been, however, largely replaced by video editing software.

Older professional mixers also used composite signals as sources. There are still some video mixer for amateur and semi-professional range and working with composite video, S-Video or even FireWire. They are often used for VJing, presentations and smaller multi- camera recordings.

Operation

The basic concept of a professional vision mixer is the bus, simply put a series of buttons, each of which is an image source. When a button is pressed, the corresponding signal is switched to the output of the bus. Older video mixer had two equal buses (A and B, such a mixer is then referred to as A / B mixer). One of these buses could be selected as the source or program bus. However, most modern mixers have a bus that is always the program bus. The second bus is then used as Vorschaubus. Such a mixer is called Flipflopmischer, because you can replace the sources of program and Vorschaubus. Both the program and the Vorschaubus usually have their own monitor.

Another striking feature of a vision mixer is called the diaphragm lever, also T - bar or Fader Bar. This lever produced, much like a Tonfader, a transition between two buses. In a Flipflopmischer the position of the diaphragm lever is actually no evidence to show which bus is active, because yes the program bus is always active (or hot) is. Rather than move the lever by hand, a button (usually "Auto Trans ") are pressed, performs the transition within a set time. Another button, usually labeled " cut", exchanges the two buses immediately and without transition. The nature of the transition can be selected in the transition section area. Major transitions are aperture (similar to the cross fading in the sound area ) and wipes, so-called Wipes.

The third bus of a vision mixer is the " Key Bus". Of these, a Vision Mixer can also have several, but in this case they share mostly a series of buttons. Here, a signal can be selected for Einkeyen. The image source will be seen, is referred to as fill, while the mask that determines the transparency of the signal is called Key. To generate this mask signal, the so-called keyer a further signal is fed in addition to the Fill signal: Key source. This is a normal video signal and often corresponds to the fill, but can also be a very different ( split function ). From the Key Source of keyer based on the type of the selected keys generated ( luminance, linear, additive or chroma key ) and the settings made (Clip, Gain, Density, Hue ) the actual punching signal, the Key. The different key types and settings are made in the key area of the mixer. Even without a key source signal keying is possible, using the most built-in pattern generator (Pattern), this provides a private stamping signal, if one selects the type to Pattern -Key. Agree fill and key source match (typically at a chroma-key ), both signals are selected simultaneously on the key bus, otherwise usually either the often known split key be maintained and then the key source signal on the Key - or Aux bus can be selected. Alternatively, there is often the option Auto-Select in the mapping Fill and Key Source on an adjustable table of the mixer is set. Typically a key is turned on and off as well as a transition. For this purpose, can be switched from program (or background ) on the Key "Transition Section".

These three main buses together form the basic mixer module called Program | Preset or P | P. Larger mixers can have multiple blocks of this kind, which are then called and numbered Mix / Effects (short M / E, often mistakenly referred to as " mixer - level " interpreted ). Each M / E section can be selected as source in the P / P section and in any other M / E, which the mixer makes much more versatile, since effects and Keys " offline " can be created and then with a single push of a button " can go on the air. "

After the P / P section there is another Keystufe called Downstreamkeyer | DSK. This is mostly used for text overlays of character generators or graphics ( eg so-called belly bands ), and has its own " Cut" and "Mix " buttons. The advantages of the classification at the end of the mixing section is that so before Downstreamkeyer still a clean, ie free from all mailing-specific graphics image can be removed, the sogenanannte Clean Feed.

After Downstreamkeyer still follows one last button, usually called Fade To Black or FTB. This acts as a " panic button " in case you accidentally applied an unrecoverable state performance mixer and an unwanted signal at the output. This button then displays the output on a black screen.

Modern vision mixers may have additional functions, such as remote control of VTRs (via a General Purpose Interface ) Aux channels for allocating resources to additional outputs, macro programming, or save the current mixer state ( " snapshot ").

All the great mixers have also for each source a so-called Tally output. This results in a signal when the source ( fully or even partially ) is switched to the output of the video mixer. This signal also is controlled on the red light cameras.

Setup and Wiring

Since vision mixers combine various sources such as tape decks and video cameras, it is very important that all these sources are properly synchronized. In professional facilities a synchronous generator generates the clock signals for all other devices. Synchrony can also be prepared by the vision mixer, a clock signal to the connected equipment sends ( genlock ). Signals that can not be synchronized (either because they come from outside the facility or because the device does not support external sync ) must go through a Time Base Corrector. Some mixers have internal "frame - syncs ", if not, you will need an additional device for it. If the video section of the mixer is used, the interface controller must (usually remotely controls the vision mixer ) are also synchronized.

Most larger vision mixers divide the sake of volume, heat and because of the shorter cable runs from the control panel of an image mixer of the actual device. The control panel is in the direction, while the main unit to which the cables are connected, is incorporated with the rest of the devices in the central equipment room.

• Television Technology