NBC NETWORK

To recap, distribution of NBC DTV network audio to affiliates is via MPEG compression built into the network mezzanine compression equipment. Affiliate stations receive up to eight PCM channels delivered on four AES pairs (stereo or LtRt plus a 5.1 channel program if it exists). It is up to the affiliate to then mix or switch local audio in, and Dolby Digital (AC-3) encode for emission.

EIGHT BASEBAND CHANNELS

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Regardless of what is actually compressing the audio, the result is simple: four AES pairs of audio are delivered to the affiliate station and these contain at minimum a stereo or LtRt signal on the first pair, then a 5.1 channel program on the last three pairs (if a 5.1 channel version is available). From this point on, the audio and video signals can be treated just like any other baseband source. At this time, there is no provision for Professional Metadata to the affiliate stations.

Some NBC affiliates have chosen to install the Linear Acoustic OCTiMAX 5.1 to add protection against wrong or missing metadata. The OCTiMAX 5.1 also fixes the long-standing problem of playing two-channel commercials out of only the Left and Right channels due to the lack of this metadata. By using the OCTiMAX 5.1, the problem is cured as local content can now correctly fill all of the channels via a simple contact closure from master control.

KEY POINTS

• Stereo or LtRt program always available on first of four AES outputs
• Baseband signals can be integrated like any other HD source
• No provision for Professional Metadata yet
• Adding a Linear Acoustic OCTiMAX 5.1 at the affiliate station can protect audio from incorrect or missing metadata and local content can be selectively upmixed to match network sound sources

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