Serving as “the island’s voice” for the Isle of Wight off the south coast of England, Vectis Radio delivers news, weather forecasts and community programming about the local economy and culture. Launched originally as an Internet-only radio stream in 2009, the station went live with their first FM broadcast on 104.6 late last year. Faced with infrastructure challenges in linking their studio to their uniquely-situated 25W transmitter, Vectis Radio bolstered the Barix audio encoder and decoder in its STL workflow with the new Barix Redundix IP audio resiliency solution.
“Our transmitter site is a rented space at a golf club on top of a hill basically in the middle of nowhere, while our studio is almost at sea level,” explained Kelvin Currie, director, Vectis Radio CIC. “We could not use a direct microwave link, as part of the hill is in the way. As dedicated private circuits were cost-prohibitive, we chose an Internet-based approach. The Barix Instreamer at our studio and Exstreamer at our transmitter site worked great right away, but I can’t say the same for the Internet connectivity between them.”
The reliable Internet Service Provider (ISP) Vectis Radio uses at its studio could not provide a high-speed connection at the transmitter location, which is far from any main communications highways. The local ISP near the transmission site put in a short microwave link to the transmitter, but like any such link, it is subject to issues like packet loss and rain fade. As a result, the station’s on-air signal initially suffered from sporadic, unpredictable audio glitches.
Working with Barix support and Andrew Nordbruch, managing director of local IT consultancy Wight Computers Ltd., Currie identified the cause of the glitches as significant, irregular packet loss on the Internet link.
“The packet loss varies considerably for no good reason,” he said. “Weather does play a factor, but we’ll sometimes experience a great amount of loss even in clear conditions. The problem was so erratic that the ISPs were unable to resolve it for us.”
Barix’s new Redundix product proved to be the ideal solution for Vectis Radio’s problem. Redundix is designed to avoid such audible glitches by repairing lost RTP packets in the audio stream using temporal redundancy on a single network link, by sending a redundant stream over a second path, or through a combination of both methods.
With just one Internet connection to the transmitter, Vectis Radio chose the time-redundant approach. A Redundix unit at the studio sends the 128Kbps, MP3-encoded RTP stream from the Instreamer encoder twice, once with a time delay; the second Redundix unit at the transmitter site effectively merges the two into a single “healed” stream. Working together, Currie and Nordbruch determined the optimal delay for their needs to be 800ms – a small latency that the station can happily live with to ensure stable, high-quality delivery.
“The Redundix units work well and clean up the transmission considerably,” said Currie. “Our packet loss is severe enough that we still get glitches on occasion, but Redundix has eliminated almost all of them and the glitches are significantly shorter too, to the point that most listeners won’t even detect them. At some point in the future we may add a second link to the transmitter site as a backup and enable Redundix’s path-based redundancy as well, which I expect would eliminate the few tiny remaining glitches.”
Currie notes that the Redundix user interface provides a lot of valuable information about the station’s network connectivity, and praises the convenience of being able to access the Barix Instreamer, Exstreamer and Redundix units through web-based interfaces for remote troubleshooting. However, most important to him is the impact that Redundix has had on his audience’s radio experience.
“Redundix has helped us overcome our biggest issue, minimizing the effects of network packet loss and thus improving our audio quality for our listeners,” he concluded.