Field Report: APT WorldCast Systems Horizon NextGen
We all know the satisfying feeling of solving a tough issue with equipment that truly works as advertized. Such is our experience at All Classical Public Media, Portland, OR, with the APT WorldCast Systems Horizon NextGen audio codec units.
The APT WorldCast Horizon NextGen with SureStream technology is a big name for the first system to provide seamless audio throughput in the presence of Internet congestion and dropouts by using two or more separate Internet circuits. We recently installed two units on a problematic public Internet link and put them through their paces. All Classical operates a small group of 100 percent simulcast FM stations and translators that require a modest-cost approach to delivering uninterrupted studio-to-transmitter program links over extended distances. Many of us in the industry have experienced only partial success with audio codecs over the open Internet, even when backing them up with redundant units, additional Internet connections and silence-sensing failover systems.
The Horizon NextGen supports multiple Internet connections with two physical Ethernet ports, and as long as at least one of the connections is receiving UDP packets from the studio, audio flows without interruption. We connect ours to separate Internet circuits, one a cable provider and the other is a DSL.
No more missed packets
SureStream allows two or more redundant streams to be sent over separate routes or networks. All streams and packets get special tagging for the decoder. At the far end the decoder inspects and synchronizes the multiple streams' latency. The decoder chooses and decodes the best packet from each stream to produce a seamless audio output. Packets may arrive out of order or be missing entirely, but as long as there is one good packet from at least one stream, all is good in the audio delivery. There are no audio drops from failover relays, glitches or other anomalies, as the SureStream decoder works its magic, choosing UDP packet by packet from the available streams.
|Performance at a glance|
|■ Multiple encoding algorithms
■ Web GUI management
■ Surestream uses redundant streams to eliminate audio dropouts
■ Opto in and relay out for remote control
■ Alarm detection for streams and networks
In STL applications where long latency is tolerable, the NextGen supports up to five seconds of buffering to provide higher immunity to packet loss. For remote broadcasts, the user can greatly shorten the latency while still enjoying the superior dropout immunity of two streams.
In the event that all streams are lost as the result of network congestion or physical cable disconnections, the NextGen recovers very quickly, typically within a few seconds. We also found that the unit operates quite well over a unidirectional IP link, such as a one-way microwave link with UDP.
The unit ships with Enhanced apt-X linear PCM algorithms. Select audio bandwidths from 3.8 to 22.5kHz in stereo and 7.6 to 22.5kHz in mono. Choose 16- or 24-bit depth.
In our station's application, Enhanced apt-X provided a good combination of high audio quality and within the modest 1.5MB/s bandwidth provided by our cable and DSL Internet services. The NextGen SureStream technology allows freedom to choose a higher stream bandwidth, because occasional dropped packets from network congestion do not create audio dropouts. Transports can be Unicast, Multiple Unicast and Multicast. Multiple Unicast and Multicast can reduce cost for multiple destinations by requiring only one encoding unit. The Horizon NextGen is also available in the lower cost IP Decoder (only) model.
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