Digital signage common sense: Digital vs. Analog signal extension (Commentary)

Sept. 28, 2012

Dave Haar

VP, Business Development-Media Distribution Solutions, ComQi

Most people, professionals and nonprofessionals alike, assume that the digital signage all around us is made up of digitally powered screens. In reality, digital signage can operate in a number of ways. We are faced with the following question: Is using digital signals necessary in deploying digital signage networks? This has turned into a relevant argument in the digital signage industry, with many vocal supporters and critics.

In order to properly analyze what type of signal is appropriate for a network, first I need to define several terms. According to Webster's online, the definition for digital is "... data in the form of especially binary digits or especially employing digital communications signals ..." Correspondingly, there are three suitable outputs that are applicable to digital signage players specifically; they include HDMI, DisplayPort and DVID signals. Again, these three interfaces need a concrete definition for the topic.

DVI, or Digital Visual Interface, was developed to create an industry standard for the transfer of digital video content. The interface is designed to transmit uncompressed digital video and can be configured to support multiple modes such as DVI-D (digital only), DVI-A (analog only), or DVI-I (digital and analog).

HDMI, for High-Definition Multimedia Interface, is a compact audio/video interface for transferring uncompressed digital audio/video data from an HDMI-compliant device ("the source") to a compatible digital audio device, computer monitor, video projector or digital television. HDMI is a digital alternative to consumer analog standards, such as radio frequency coaxial cable, composite video, S-Video, SCART, component video or VGA.

DisplayPort is a digital display interface primarily used to connect a video source to a display device such as a computer monitor, though it can also be used to transmit audio, USB and other forms of data. It is designed to replace VGA, DVI and LVDS by creating a high-performance standard. Although DisplayPort supports much of the same functionality as HDMI, it is expected to complement the interface, not replace it.

Now that we have a better understanding of digital signals and the three outputs, next we will evaluate the benefits of digital signals to the network. The first benefit of a digital signal is that the quality and depth of the picture color is maintained, whereas that of an analog signal is inconsistent. An organization is recognized through its brand, and thus a digital signage network needs to be reliable in displaying the brand colors. For instance, with digital signals, the "Coke red" on screen A will be exactly the same as the "Coke red" on screen B. The next advantage is difficult to identify: We don't see much of a gain in distance, resolution and price through digital signal.

On the other hand, we do see an advantage using analog signals versus digital signals in some dimensions. According to online references (such as, Category 2 HDMI cables can be effective to distances of about 50 feet. HDMI extenders range from 100-800 feet, depending on whether they are using single or dual CATX cable and up to 1000 feet using fiber. At HD resolutions (1920 X 1080), DVI cables max out at about 15 feet and DisplayPort cables at about 40 feet. Both DisplayPort and DVI Extenders max out at 330 feet at HD (1080P) resolutions. HD analog signals, by several manufacturers, can support distances of up to 2000 feet over copper, and several miles over fiber. Hence, distance has the advantage using Analog systems. Another example of analog's positive influence in distance is in environments where multiple screens are showing the same content due to the cost savings on players and licensing fees by having fewer players to cover the equivalent distance.

Another major advantage of analog over distance is the resistance to interference, while many DVI and HDMI extenders have issues with RF and other radio frequencies. Landmark Theaters' recent deployments of the analog networks are a classic example of switching from digital to analog after experiencing performance issues.

Analog devices from digital signage players and from VGA, DVIi and DisplayPort can all support up to 1080p resolution, thus resolution can be removed from the equation for our analysis.

Finally, cost is the last metric to compare. Creating content in 1080p resolution versus 720p or lower has a higher cost due to the cost of equipment as well as the process of extending the signals from the players to the screens. The following chart displays the average of on-line prices at maximum cable lengths for digital versus analog resolutions.


Analog extension and distribution equipment costs are significantly less expensive than digital extenders and distribution amplifiers. They will go significantly longer distances, without needing to revert to fiber. Even without using extension, cables for digital devices are more expensive than analog.

Based on the above analysis, it is safe for me to conclude that digital output to digital signs has a place in current and future deployments, especially as network streaming-based and HDBaseT-based systems become more prevalent. However, network owners and operators should still consider an analog system if they are concerned about lowering both capital expenditures as well as operating costs over the life of their networks. Analog will be relevant for a long time due to its definitive benefits that this article pointed out. Other issues, not discussed, such as locking connectors, are proof that analog is still a strong choice. Finally, I would love to collect the thoughts of the audience on the subject. Does the rest of the industry feel the same way?

Chime in with your thought in the comment section below.

ComQi is a provider of multichannel message management in the digital signage and digital out-of-home industries, providing content and network management platforms along with media distribution technologies.

Read more about digital signage networks.

Topics: Content Management , Hardware , Networks

Companies: ComQi, Inc.

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