Linear Acoustic helps Tribune insert local DTV audio at station level

Linear Acoustics’ StreamStacker enables stations to easily and cost-effectively splice local audio into the output transport stream.font>

Linear Acoustic has designed and implemented a new system for Tribune Broadcasting that allows its stations to insert local audio elements into a network-supplied DTV stream. The system, which leverages Linear’s StreamStacker product, was used for the first time earlier this month for the premiere broadcast of the “Lord of The Rings” on Tribune’s 19 WB Network-affiliated stations. The product enabled the stations to splice local audio into the output transport stream.

The StreamStacker encodes all audio channels and associated metadata at the station and passes it unchanged through the distribution system to the consumer. It also provides 5.1 channel surround sound, alternate language secondary audio programs (SAP) and descriptive visual service (DVS) capabilities. Many stations have used Dolby E encoding and high-rate AC-3 (Dolby Digital).

The system can combine up to four 5.1 channel AC-3 encoded programs into a single AES pair. More than 20 channels will fit in the same space required for eight channels in Dolby E.

At the local station, the stacked stream is separated into its original programs and the AC-3 streams are inserted using StreamStacker. This allows local audio switching without compression cycles or affecting the metadata structure.

The system can also manage AC-3 audio within a DVB-ASI transport stream. Stacked AC-3 streams are fully-compatible with all Dolby-certified AC-3 decoders. With StreamStacker four AC-3 programs of mixed data rates/channel count can be connected and the system will synchronize and stack them into a single 48kHz AES stream.

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