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Converting Video: A Look at Hardware D/A Converters

By Ron Seifried

In all levels of production, whether it is for broadcast, industrial, event videography, or home movies, the one item that has become a major component for video is the converter. The external video converter is a device that receives a video and/or audio signal and outputs an entirely different signal that conforms to the production needs. This can encompass Digital to Analog (DAC) or Analog to Digital (ADC), converting between analog voltage and digital numbers.

In video, if you want to take a signal from a digital source like DV and display it on an analog monitor, a converter is mandatory. The reverse process would be required if you want to capture analog footage into a computer for editing. Many of today's converters are bi-directional, eliminating the need stack up more than one piece in a studio. With audio, MP3's and CD's are in digital format, yet speakers are output from an A/V Receiver, an analog source. Higher-end stereo systems convert signals to a pre-amp and may be able to interface with a USB device.

With the advent of the Digital Signal Processor (DSP), analog signals are converted into digital bits via a microprocessor that speeds up the processing. Texas Instruments is the main architect of DSP's, with designs including codec's, filters, and digital/analog converters. DSP's are behind the scenes of what we take for granted in, including RADAR, SONAR, biomedicine, weather and economic forecasts, CAT scans and MRI, and of course, video/audio processing and compression.

Some important terms you will need to know before deciding on what type of converter you need:

A full size HD Image

Upconverting: Used in both video converters and video scalers, this is the process of taking low -resolution video and increasing it to a higher resolution video, using algorithms to copy parts of surrounding pixels, and interpolate what the footage should look like at a higher resolution. The picture does not actually become more detailed. This process allows a standard-definition video to display on a high-definition monitor without any viewable blank spots. The end result is an improved picture, but not the superior quality of high definition. Because of the limitations of the final picture, it is important to make sure that the original footage is of very good quality, in its native aspect ratio, with minimal artifacting and noise. Anything less, including letterbox, will greatly diminish the final output.

The image on left is in SD resolution, on the right is HD. Notice the aliasing in the SD image on the left compared to the HD image 

Downconverting: Going in the opposite direction, downconverters convert high-definition video to standard definition. When watching most programs on broadcast standard definition TV in letterbox, chances are that the video has been downconverted from high definition. Because HD is playing back in either 720 or 1080 lines of resolution, standard defintion needs to eliminate the extra information to play back in 480 lines. Downconverters come in many forms, but the better the downconverter, the least amount of aliasing, noise, or blurring will occur.

There are methods of upconverting and downconverting video, with software using programs like Adobe After Effects, but this article will focus on hardware video/audio converters only.

Aja FS-1

Aja FS-1 comes in a 1U rack

Aja has been in the forefront of A/D converters for years, with over 30 different models available. Introduced at NAB 2007, the FS-1 is able to output simultaneously in HD and SD video while supporting most common connectors. Working in 10-bit Broadcast quality video and 24-bit audio, the FS-1 can also upconvert SD to HD or downconvert HD to SD. With the few HD formats out there today, the FS-1 can easily cross-convert between the formats as well as output at the same time. Balanced analog, 8-channel AES and embedded audio round out the I/O's with support for networks, including SNMP monitoring and web-based remote access.

Barco Image PRO converters

Barco converter's are available in three models: Image PRO, Image PRO-SDI and Image PRO-HD.

Barco's family of Image PRO converters has high-performance features, including aspect ratio conversion, Genlock, motion adaptive de-interlacing, and 3:2 and 2:2 pulldown detection. The Image PRO is a scan converter, video scaler, switcher, and transcoder, with a wide range of image format compatibility including RGB, HDTV, component, s-video, composite, DVI, SDI, and HD/SDI.

The Convergent Design HD

The latest from Convergent Design

The Convergent Design HD Connect MX ingests HDV, DV, and AVCHD into an SDI-based editing system and de-embeds AES audio and LTC Timecode from HDMI. Video shot with consumer camcorders can be compatible with higher end editing suites with real-time conversion of HDV to DNxHD, DVCPro and I-Frame codecs; long-GOP editing is no longer required. Convergent Design also has the nanoView, a converter for HD/SD-SDI to HDMI connection for monitoring HD projects on Plasma displays.

Pyro AV line

The newly branded Pyro AV line

Created as the Broadcast Solution of ADS Technologies, Pyro AV recently announced three new converters at NAB 2007. The SD10DAC converts 10 bit SDI to composite, s-video, or component in NTSC or PAL. The HD10DAC converts 10 bit SDI (4:2:2 and 4:4:4) to full bandwidth HD component, s-video, and composite. The HD12ADC ups the ante of the HD10DAC by supporting 1920 x 1080i 60 and using 12 bit ADC's to generate two duplicate SDI video streams. Both HD models have multi-rate serializers for either SD-SDI or HD-SDI conversion.

Blackmagic HDLink Pro

The Blackmagic HDLink Pro is able to output video and audio via the HDMI connector

The Blackmagic HDLink Pro is a HDTV resolution monitoring converter for DVI and HDMI monitors that switches between SD-SDI, HD-SDI (4:2:2 and 4:4:4) and 2K (SDI). The introduction of 3 Gb/s SDI for high-resolution 2K film monitoring on a large 30-inch (2560 x 1600) DVI display ensures that editors are able to monitor 5.1 surround sound with six separate audio channel output. The new color management tool with built-in 3D lookup tables, and enables editors to see simulated film output for the correct color levels and automatically configure to most connected displays.

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