Transcript
A/V Technology: When to Switch, Extend, Convert and Distribute
With the multitude of audio/video devices and the innumerable number of audio/video application situations, additional electronics are often required. This article will explain the use of and provide examples for when to switch, convert, extend and distribute audio/video signals. An audio/video switch is an electronic device which allows multiple source devices to connect to a single display. These devices physically switch between inputs by either automatically detecting a signal from a connected device, or manually through buttons, IR, or serial commands. A basic audio/video switch will have multiple inputs and a single output. Typically, this type of device will require that all connected devices support the same signal or signals. For example a four port VGA video switch will have four separate VGA video inputs and a single VGA video output. Specialized switches are available and allow for either multiple inputs/outputs or support multiple signal formats. An A/V matrix switch supports multiple inputs, like a regular switch, but also supports multiple outputs. This allows any of the connected source devices to be displayed on any of the displays connected to the outputs. Switches that support multiple signal formats, like a connectivity panel, typically include a signal converter which allows all of the various inputs signals to be output as a single signal type. For example a connectivity panel may offer HDMI®, VGA and audio, composite video and audio, and iPod® video and audio, as inputs and offer a single HDMI audio and video output. An audio/video switch is generally used for any situation where there are more source devices being used than there are inputs on a display. An example of a typical application where a switch would be used is in a school environment. Teachers often require that multiple devices, i.e. laptop, desktop, and document camera, that must be displayed through the classroom’s projector. If the projector does not have an adequate number of inputs to accommodate these devices, then a switch would be required. The rapid advancements in the technology used for audio/video devices and the current trend of A/V manufacturers who are phasing out analog outputs, have created many situations where the outputs of A/V source devices do not match the inputs of A/V displays. When this situation arises, it is typically necessary to use an A/V converter. A converter is an electronic device which alters a video signal so that the output signal is different from the input signal. A common need for signal conversion occurs when a legacy or older device must be used with a modern display. Older A/V devices typically produced analog signals, while modern displays often use digital inputs. It is not possible to passively adapt an analog signal source device to the input of a digital display because of the fundamental difference between analog and digital signal types. Analog A/V signals are composed of varying amplitudes and wavelengths of electrical signals. Digital signals are composed of a set of discrete values, i.e. “on and off”, or “1 and 0”. Because of this fundamental difference between the signal types, active signal conversion is required to connect an analog source to a digital display or vice versa. An example of a typical application where a converter would be required would be a house of worship that purchased a new projector, but still wanted to utilize their older computer. The VGA output of the computer would need to be converted to HDMI so that the image could be displayed on the new projector. Signal extension is often a requirement in A/V applications where the source device is not capable of pushing the A/V signal over the length of cable used to connect the display. The maximum supported signal distance will vary depending upon the signal type generated by the source device. There are many official and unofficial length limitations for the various types of A/V signals. See the chart below showing the limitations of many common signal types: Official length limitations: These are standards that have been defined by industry associations. DisplayPort™ — 15 meters (about 49 feet) DVI digital — 5 meters (about 16.5 feet) Ethernet (CAT 5e/6/6a) — 100 meters (about 328 feet) FireWire® (also called IEEE-1394, DV, and iLink™) — 4.5 meters (about 15 feet)
Parallel (IEEE-1284 compliant cables) — 10 meters (about 32.5 feet) SCSI (single-ended) — 6 meters for SCSI-1 and SCSI-2, 1.5 meters for SCSI-3 SCSI (differential) — 25 meters USB — 5 meters (about 16.5 feet) Ultra-ATA (also called IDE) — 18 inches, with no more than 6 inches between devices Unofficial length limitations: These signaling methods do not have a defined maximum length. The limitations listed here are based on common real world experience. Please use these as a guideline—the application may allow for a longer cable run, or may call for a shorter distance. Check with the equipment manufacturer for a maximum supported cable length for each individual device. The best advice for these types of cables is to use the shortest cable possible. Audio (line level) — 150 feet Audio (speaker level) — 500 feet (use lower gauge wire as distance increases) Audio (digital coax) — 50 feet Audio (digital optical) — 5 meters (about 16.5 feet) Component video — 150 feet Composite video — 150 feet Ethernet (Fiber optic) — up to several kilometers Keyboard (PS/2) — 25 feet HDMI® — 5m (about 16.4 feet) without a booster Modulated RF (CATV, SATV) — 150 feet (use RG6 coaxial wire) Mouse (PS/2) — 25 feet without a booster S-video — 150 feet Serial (RS232) — 1000 feet VGA (Laptop output) —35-50 feet without a booster/amplifier VGA (Desktop output) —75-100 feet without a booster/amplifier
When an application requires cable lengths that exceed these limitations, it is necessary to use an extension device. Extension devices may be either active or passive. Passive extenders use transformers, while active extenders use powered amplifiers and active devices to offer equalization. The choice of whether to use passive or active extension devices depends upon many factors, including the length of the extension, the type of signal, and the video quality expectation. An example of when an extender would be used is in an auditorium where a computer in the podium is located 150 feet away from the projector. An active VGA extender would be used to connect the VGA output of the computer to the VGA input on the projector. There are a variety of applications that require the signal from a single source device to be displayed on multiple monitors. These applications typically require the use of an active device such as a distribution amplifier. A distribution amplifier will accept a single input and will output that signal to multiple monitors. These devices often use a principle called unity gain. Unity gain is a type of amplification where both the input and outputs are at the same voltage level and impedance. An example of when a signal would need to be distributed would be in the waiting room of a physician’s office where a computer is used to support a digital signage system. A VGA distribution amplifier would be used to distribute the VGA signal from the computer to multiple monitors throughout the waiting room.
Switch
Convert
Extend
Distribute
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