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Blog Central

Channeling Your Inner SDI

Posted by Shane Toven on Dec 14, 2016 2:06:18 PM

AERO.100 DTV Audio ProcessorBuilding on insight and history in the television broadcast industry, The Telos Alliance created a new division to focus on the expanding needs of the TV audio market. Titled the “TV Solutions Group” (TVSG), the knowledge and resources of the two Telos Alliance TV brands, Linear Acoustic and Minnetonka Audio, are combined to provide a wide range of products, solutions, consultation, and custom development. Read more about TVSG here.

Here's the first of many TVSG tech tips:

SDI. It seems so simple and elegant, right? Video along with 16 channels of embedded audio on a single coaxial cable. That’s great, until you realize that those 16 channels of audio could be carrying anything from a single stereo audio pair, up to multiple 5.1 mixes, downmixes, and perhaps even Dolby encoded audio—in any number of channel configurations.

In a perfect world everyone would always use the same channel assignments, but we know that ain’t gonna happen. Generally, the first 8 channels would be Lf, Rf, C, LFE, Ls, Rs, then perhaps a stereo downmix—but some sources (for example) provide a downmix on the first two channels, followed by a 5.1 mix on the next 6 channels. So what can you do if your plant follows a different standard?

Current AERO processors provide the ability to shuffle channel pairs however you see fit, both on input and output. Change the channel order feeding a processing instance by going to “Home > Instance x > Input > Source” through NfRemote—and remember that the AERO processing instances generally expect a “standard” channel order of Lf, Rf, C, LFE, Ls, Rs on their inputs when processing a 5.1 signal. When processing stereo audio, they expect to see it on the first input pair of a 5.1 program, or 7/8, or 9/10 for additional programs in a DRC instance. When upmixing from stereo to 5.1, the stereo content must ONLY be present on the first input pair—otherwise it will be treated as 5.1 and not upmixed.

Now that we’ve talked about the input side of the equation, let’s get that audio back out of the box. In NfRemote, navigate to “Home > Output Routing > AES/SDI Out”. From there, you can assign the outputs of the various processing paths (or Dolby encoders if applicable) to the AES and SDI outputs. It’s worth mentioning that current AERO processors also allow routing UNPROCESSED audio to the SDI outputs through “Home > System > I/O Setup > SDI Embedding”. This controls the actual SDI embedding and would normally be set to the corresponding processing path. In earlier products such as AERO.one, it was necessary to route the AES output to the SDI channel pair to embed processed audio—but that is no longer the case with current products. Make sure that you are actually routing what you THINK you’re routing.

As always, our support team is happy to ponder your channel assignment quandaries and help you untangle it all. Give us a call at 717-735-3611, or e-mail support@linearacoustic.com.

Topics: Linear Acoustic, Television Audio, Aero.100