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Black Box Explains...Upgrading from VGA to DVI video

Analog video (VGA)

An analog signal is continuously variable. Composite video, Component video, RGBHV, and VGA are types of analog video signals, with VGA being the most common video format used with PCs — at least until recently.

An analog video signal can be run over long lengths of native VGA cable as long as the diameter and shielding of the cable are good enough. However, regardless of the cable quality, signal attenuation increases with video frequency and cable length. This means that after 30 to 50 feet, the image quality will start to degrade. This leads to color skew and smeared-looking text. To solve for signal degradation in VGA applications, use an extender that compensates for signal loss. A good extender has separate adjustments for high and low frequencies; HF loss is usually greater than LF loss.

Digital video

While analog video signals travel in a sine-like wave form, digital signals travel in a square-like waveform. A digital signal is broken into a binary format where the audio or video data is represented by a series of 1s and 0s. Like analog signals, digital video also suffers from loss, but as long as the cable is of sufficient quality and within the maximum supported distance, the signals don't suffer from blurring or color skew. 

However, what you will get when the maximum supported cable length is exceeded is the “cliff” effect, where the digital signal drops off and the picture is completely lost. To overcome distance limitations, use extenders or repeaters.

Digital Video Interface (DVI)

DVI is the standard digital interface for PCs.The DVI standard is based on transition- minimized differential signaling (TMDS). DVI comes in two formats: single-link and dual-link. Single-link DVI has a maximum frequency of 165 MHz, and dual-link DVI, as one would expect, has double the maximum frequency. A single-link interface can transmit a resolution of 1920 x 1200 vs. 2560 x 1600 for dual link.

The most common DVI connectors are:

  • DVI-D: A digital-only connector for use between a digital video source and monitors. DVI-D eliminates the analog signals.
  • DVI-I (integrated): Supports both digital and analog RGB connections. It can transmit either a digital-to-digital signal or an analog-to-analog signal. It is used on products instead of separate analog and digital connectors.