What's New in Program Distribution?


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Case #4

In 2010, Rick Hunt, the VP and director of radio engineering for Entravision, started looking for a replacement for their legacy SCPC satellite distribution system. Entravision already had AT&T MPLS circuits between their Los Angeles facility and each of their local markets; these were used to move commercial audio content in addition to accounting and sales information, among other things.

Late in 2010, Hunt started testing IP multicast with the Comrex Access on the Entravision MPLS network; by the middle of 2011, he began operating the MPLS distribution in parallel with the satellite network. By the end of last year, the new system had proven itself; Entravision was able to terminate their satellite contract then, saving the company several hundred thousand dollars in yearly operating expense.

Comrex Access (rack mount) units are used to originate the multicast streams from Los Angeles. This is a 1RU, full-duplex codec with a single Ethernet port (used for both streaming and management). In addition, with the appropriate physical-layer interfaces, it will work over 802.11b, g or n Wi-Fi, and 3G or 4G cellular networks such as EVDO, UMTS, WiMax and LTE. Codec algorithms available for use with Access are Comrex's proprietary BRIC HQ1, HQ2, and ULB (ultra-low bitrate). Linear, FLAC, G.722, G.711, AAC, HE-AAC, HE-AACv2, AAC-LD and AAC-ELD are also included. The Access has line-level XLR balanced analog inputs and outputs, as well as AES3 balanced XLR ins/outs. GPIO access for four remote contact closures is available via a DB9 connector on the rear apron.

The Comrex BRIC-Link is used by Entravision on the receive end of the IP multicast streams. This is a 1RU, half-width full-duplex codec, using 1/4" TRS connectors for balanced line-level audio inputs/outputs. (AES inputs/outputs use the same connectors.) It has a single Ethernet port, used for the streaming and management; GPIO is available via a mini-DIN, as is the serial port. The power supply is an external unit. The included codec algorithms are linear, FLAC, AAC, HE-AAC and HE-AACv2, G.711 and G.722.

Entravision distributes multiple networks to more than 70 stations via IP Multicast; these include the Tricolor Network; the Maria Network, the Jose Network, and specialty programs such as "Contacto Directo con Jenni Rivera" and "El Vacilon del Mandril," among others. The standard data rate for the streams is 160kb/s, AAC, stereo. According to Hunt, the audio quality far exceeds that of the old SCPC network.

Entravision also distributes programs to affiliate stations by way of multiple-unicast streams. These connections are made via their ISPs in Los Angeles (they have two -- one is available as an immediate backup to the main). The affiliates use all kinds of Internet services, even DSL, to receive programming.

Whether you have put together an ad-hoc network of a half dozen ISDN codecs to distribute a morning show, or if you distribute 24/7/365 programming streams, or something in between, it's probably worth your while to learn more about this technology. It may provide a useful alternative for your current operation, now or sometime in the future.


Irwin is transmission systems supervisor for Clear Channel NYC and chief engineer of WKTU, New York. Contact him at doug@dougirwin.net.




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