MultiMerge at KENS-DT
Sep 1, 2008 12:00 PM, By Jerry Paonessa
Neural Audio's processor solved this station's issue of 2.0 audio interspersed in 5.1 surround programs.
Like many other television outlets transitioning to digital transmission, KENS-DT was facing the dilemma of keeping audio properly distributed in our transmission feed. The San Antonio, TX, CBS TV affiliate station had to integrate regular stereo content with 5.1 surround material that was being transmitted in the CBS network feed.
The DTV station's technical configuration is fairly simple. The station has a pair of Harris HD IRDs provided by CBS, a pair of Dolby DP-572 Dolby E decoders and a Dolby DP-569 digital audio encoder, all ahead of a Harris Flexicoder and an Evertz 12 × 2 router as a DTV master control switcher. All of the DTV switching is done under Sundance automation control. Doing metadata switching between network and local programming was not so difficult. The problem was how to deal with 2.0 content that CBS itself would intersperse through the 5.1 surround audio in the program.
The options
In order to solve the dissonance in the transition between the stereo and Dolby content, the engineering staff initially attempted to extract external metadata from the incoming signal and apply it to the final audio encoder, a DP-569. We connected a cable from the “metadata out” port on the DP-572 and connected it to the “metadata in” port on the DP-569. That worked for a while, until CBS became more sophisticated in its switching methods. After that update, if we persisted in using the metadata extraction method, the encoder would often fail to switch back to 5.1 surround from 2.0 stereo. That left us with nothing but the front surround channels on the air instead of the full 5.1 surround.
Figure 1. Neural-THX Surround MultiMerge + Neural Loudness Control (NLC) setup.
Click to enlarge
Another alternative to automatic metadata switching left the encoder in 3/2L mode all the time, causing dramatic spatial and level shifts whenever the program content changed between 5.1 surround material and 2.0 stereo commercials and local content. This was unacceptable.
The team also fired a GPI closure during stereo programming, switching the audio encoder into its 2.0 mode. This at least was better than allowing the broadcast audio content to be all over the landscape, so to speak. Although, it introduced another manual operation to an operator's already busy workload.
By mid-2005, the station's engineering team had no idea how to automatically transition between mixed audio formats. The thought of using mixers and surround audio detectors was not appealing and would have been a primitive solution at best. Plus there was no solution to the problem of how to reliably record HD content with 5.1 surround audio for delayed broadcast.
Then, Reed Wilson, an A. H. Belo technology manager, suggested a solution that was successful for WFAA-TV in Dallas. The Neural-THX Surround MultiMerge from Neural Audio is a way to automatically and seamlessly switch between 2.0 and 5.1 audio content.
The install and setup
My initial research on the MultiMerge suggested that it was a plug-and-play device. We would simply switch it on and place it in the digital audio stream between the multichannel output of our master control switcher and the input of the Dolby audio encoder. The unit would do the rest. We set up a range of inputs and outputs on our audio patch panel and awaited delivery of the device.
As with any digital device requiring synchronization between audio and video, it is important to provide AES reference to the Neural-THX. With a stable reference, you can be certain the lip-sync adjustments remain where you put them. The station team used a standard AES silence at 48KHz applied to the word clock input on the back of the unit.
The setup illustration in Figure 1 above shows the MMC-100 (MasterPlus) AES audio outputs as they pass through one jack field onto the audio processor and finally to the DP-569. For EAS events, the DP-569 is switched to 2.0 stereo operation through a GPI closure to pass EAS audio from the TFT 999, and it is switched back to a Neural 5.1 preset (which we created) once the EAS event concludes.
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