Playout Normalisation
Playout systems are typically designed to work best with one standard type of files. Files from suppliers come in a wide range of types. File “Normalising” is the process of converting all of those input formats in to the required standard type needed for playout.
The most common playout format used by our customers is 8 channel MXF files, that are encoded as Stereo PCM, Dolby E, Stereo PCM and Dolby E.
Our playout customers tell us they generally receive files with 2 channels, 4 channels or 8 channels, and less commonly with 6 channels. This leads to four requirements being almost universal.
- Increase the number of channels to 8
- Loudness correct the incoming audio
- Dolby E encode the stereo PCM if no Dolby E is present
- Duplicate source channels or the encoded Dolby E to create the required output structure
In concept, Engine splits the audio away from the video and metadata in the source file, does Loudness processing and Dolby E encoding. Then the processed audio is merged back with the video and metadata, with extra audio channels being added as needed, and the required channel mapping is created.
A lot of companies do at least part of this normalisation process by hand, in costly Edit suites, but the process can be entirely automated using Engine.
Start with Engine’s easy to use graphical editor and create a workflow for a normalisation process. The following example starts with a 2 channel file containing only PCM stereo, and ends up with the required format and layout. Engine is used to apply Loudness correction to EBU R128, although of course other standards such as A85 and TR-B32 could be used. The compliant audio is Dolby E encoded, then everything is placed in to the correct channels.
This next example is for source files containing four channels, with a PCM stereo and a Dolby E pair. Even though the second pair contains Dolby E, the loudness correction will still take place automatically without needing a specific decode/encode stage. As with the first example, the channels are duplicated to the required locations in the new 8 channel structure.
The following video demonstrates how to create a Playout Normalisation workflow using Engine.
Engine’s conditional workflow feature lets you choose the required workflow based upon the number of channels in the source file. It can also be used to run a different set of workflows if the source files already contain Dolby E, or if they do not. Therefore Engine can detect the presence of Dolby E, and if not found it can encode a Dolby E track from the main PCM stereo. You can also specify different workflows depending on the channel layout within the Dolby E audio.
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