Audio engineering inherently begs two simple, yet necessary questions: How do we get audio from here to there? And will it sound good? Telephone hybrids, POTS codecs, RPU transmitters and ISDN have been staple routes for getting audio in and out of the studio. Some studios even have the luxury of having hard copper lines installed. With the right amount of impedance matching and luck, a clean audio feed is attainable. But when the copper gets old and the signal becomes marginal, it's time to look elsewhere for cost-effective remote audio retrieval.
Such is the case at Victory 88.3 FM, the 50kW flagship station of the Flames Sports Network, which broadcasts Liberty University football and men's basketball games. Both athletic arenas are built on the same campus as the station, and engineers in the mid-1980s made game time audio available using copper telephone lines that were already in place. By cross-connecting around the campus Lucent switch, one-mile balanced audio feeds were established. This worked well until 2005, when the aging lines became too noisy to satisfy a critical listening ear. No amount of impedance matching seemed to work. The copper was simply too old (and wet). When the university IT technicians told me that our IP network was reliable for audio transfer, the audio over IP idea began to stir in my head.
Inside the box
Barix manufactures TCP/IP-based network amplified audio products that can be used within local area networks and over the Internet. I chose the Barix Instreamer and Exstreamer Gold to connect the Victory FM studios to the broadcast booth at Williams Stadium for football broadcasts. The Instreamer can be thought of as the transmitter and the Extreamer a receiver. Put simply, when connected to a network (standard RJ-45 network connection) the local network dynamic-host-configuration-protocol (DHCP) server allocates an IP address to each unit. When a DHCP server is not available, Barix uses the IPzator function to search the network for an available IP address. A supplied ear bud allows the user to listen for a friendly voice to recite the address on power-up. This feature is known as Sonic IP, and it helps to have pen and paper in hand to write down the announced address.
Performance at a glance
Controlled via Web browser or IR remote control
Encodes and decodes MP3
IP or RS-232 control
Connects via any IP link
Unbalanced RCA and S/PDIF I/O
Once the IP addresses are established, while within the same network, type the address in a browser (for example, http://10.40.51.32). A comprehensive online interface allows for control of each unit. The only physical control on the Instreamer and Exstreamer is a reset button. Otherwise, you have full real-time control via the LAN.
The audio inputs and outputs connect via stereo RCA or coaxial S/PDIF, which qualifies the Instreamer and Exstreamer as a prosumer solution to IP-based audio transfer. However, general managers and engineers agree that clean, affordable audio transfer is a must for radio as well. The audio stream is MPEG Layer III, and the sample rate and compression is configurable. The bandwidth requirements, depending on the configuration and selected audio quality, are between about 40kb/s and 107kb/s. When the Instreamer and Exstreamer connect to each other, there is noticeable (but normally negligible) delay depending on buffer settings. Of course, traffic and stability can affect the performance of any device connected to a network.
The Instreamer comes with a stereo ear bud, which allows for monitoring the input level of the audio and announced IP address. The Exstreamer also has an ear bud that plugs into the analog RCA output for hearing the announced IP address. When the Exstreamer is permanently installed, an infrared remote control allows for easy volume and playlist adjustments (the Exstreamer can also interface with a PC or audio server to stream playlists). Changes to network settings, audio and streaming adjustments on both units are made through the online interface.
I have not experimented thus far with inter-network connections, but the university IT people tell me that through cooperation with other IT networks, firewall and IP address assignments it can be set up to allow for long distance remotes. In our case, when the Liberty University football team is on the road, we can take the Instreamer to other campuses.
The Exstreamer offers flexible options that allow for setups based on personal preference or network configuration. Using the Zserver feature, the Exstreamer will play music from playlists on any PC on the network or a Web server. The unit can be set up as a stream “puller” or stream “receiver.” Also, in situations where a network connection is not available for configuring the unit, a supplied serial cable allows for RS-232 connection through a PC port.
The Instreamer shares its configuration flexibilities with the Exstreamer. The Instreamer can serve as a shoutcast/icecast source. Also, audio players such as Winamp or Windows Media Player will play audio originating from the Instreamer. This is a great technique for monitoring the unit, or for listening to remote playlists.
While the Barix design concept accommodates consumer-based installations, the Instreamer and Exstreamer are well suited for radio stations that need to move audio in real-time. If the program material can withstand data compression, the MP3 stream provided by Barix is more than sufficient. Using a critical ear, I have not heard digital artifacts or jitter that degrades program material.
Wygal is the programmer, engineer and Web designer for WRVL in Lynchburg, VA.
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