NEW BERN, NC, USA (July 29, 2013) – A Minneapolis station became the first to broadcast with an all-digital air chain using Wheatstone® baseband192 technology into their Nautel transmitter, marking an historical event in radio transmission.
Northern Lights’ KTWN-FM (96.3) went on the air with Wheatstone’s new AirAura X3 audio processor Thursday, clearing the last obstacle to a 100% digital air chain by using the processor’s new baseband192 interface into a Nautel transmitter.
Wheatstone baseband192 is an open standard technology that eliminates the need for an analog composite interface between processing and transmission. Offering AES-EBU output into FM transmitters now equipped with a digital baseband input, the baseband192 interface is available as a standard feature in Wheatstone AirAura X3, FM-531HD and VP-8IP audio processors.
“Up until now, the technology didn’t exist to give us the digital connectivity between the processor and the transmitter without it affecting on-air loudness,” said Northern Lights engineering manager Rob Goldberg, who worked with broadcast colleague Mike Oberg to achieve a loud, yet detailed sound from the AirAura X3.
Unlike other approaches, baseband192 digitizes the entire multiplex spectrum including the RDS and SCAs up to 67 kHz for direct AES-EBU into the FM exciter. Unique to baseband192 is the ability to piggyback the RDS and SCA signals in digital form, eliminating the need to re-route these signals directly to the FM exciter instead of passing RDS and SCA signals through the processor (as is the practice without the digital multiplex interface). A single AES-EBU cable between the Wheatstone processor and the transmitter carries the baseband signal, bypassing the need for multiplexing in the exciter and eliminating the resulting signal overshoot and associated loudness tradeoff. Because the baseband192 signal encompasses the entire multiplex spectrum after stereo generation, it also includes any loudness increases that may have been contributed by the FM processor’s composite clipper.
“We are finally opening the door to a completely digital air chain, from the audio playout system to the transmitter’s digital FM modulator,” said Jeff Keith, Wheatstone senior product design engineer, adding that baseband192 was built into the original AirAura four years ago but had been held back until FM transmitter manufacturers could offer a digital multiplex interface to their transmitters. At the recent NAB 2013 convention, transmitter manufacturers announced upgrades to their FM exciters that could accept the necessary digital multiplex signal.
The data format that transmitter manufacturers chose is a high-speed version of AES3 in which the stereo multiplex spectrum is handed to the exciter as a 192 kHz AES3-formatted signal. Baseband192 provides a digital multiplex output using the FM processing chain’s AES3 digital output. In addition to other benefits, standardizing on this format allows for maximum flexibility around the broadcast plant because it uses standard 110 ohm balanced digital cables and familiar XLR connectors.