Copyright ©1997, RF Specialties Group.
An old road
warrior, the regular phone line, appears to be back in the running for remotes
and field reporting. In this incarnation it's called a Plain Old Telephone Service
(POTS) codec, a way to digitally transmit audio over regular phone lines using
the standard computer modem and audio compression. As of this writing, Comrex
and Marti have completed beta testing with production units expected in January
and Musicam USA just started shipping its ISO/MPEG Layer III version of POTS Codec
in October.
The most likely applications for this device are last-minute remotes and on-the-spot field reporting. Of course, there are better vehicles on the road today, and broadcasters should soup up their remotes and news reports with ISDN, radio links, perhaps even spread spectrum devices. But, when the only thing around is a phone line, POTS codec offers bi-directional wideband mono audio varying from 4.5 to 10kHz.
Robert Meuser, chief engineer of WHTZ FM, New York, is testing several POTS codec units for those situations in which ISDN, the station's link of choice, is not available. His experience is that the average telephone service connect speed is around 22 to 24 kilobaud, although 2,400 baud isn't unheard of, especially in older residential areas. Under ideal conditions, POTS codec units deliver up to 10kHz audio. Some will operate as low as 12 kilobaud, but cut off the audio at around 4.5 kHz; anything below this threshold is not enough bits for the audio compression. Marti's unit will even ratchet back to hybrid analog operation automatically at connect speeds below its minimum threshold.
Although the POTS codec devices Meuser tried are, to varying degrees, quick, easy to set up (easy enough for talent to use in the field, he said), and very cost effective with bi-directional capability on one phone line, he would recommend sophisticated mix-minus setups at the studio, as up to a half-second delay in each direction can be experienced. With error rates over POTS unpredictable from region to region, and synchronous, real-time operation a must for broadcasters, both Marti's Smarti and Musicam USA's FieldFone( use the low bit extension of the Layer III algorithm, and Comrex's HotLine uses a proprietary algorithm developed for the low connect speeds of POTS and a typical eighth-of-a-second delay one way.
Marti
also offers the user a choice of the G.728 algorithm, so stations can use this
for the auxiliary talkback feed, on which some audio quality can be traded for
a shorter delay. G.728 and G.722, the compression scheme available in at least
one foreign-made POTS codec, have shorter delays but are notorious for falling
apart when background ambiance is introduced, according to Art Constantine of
Musicam USA. "If I'm CBS calling in from the war zone, I want to hear those
bombs dropping," he said.
And, in fact, two news groups did report from the proverbial war zone the night of the presidential election using POTS codec, WCBS in New York using the Musicam USA Layer III FieldFone and MSNBC in Washington state using the Comrex HotLine. Given that the Republican camp and Democrat Carolyn McCarthy hadn't announced where they'd hold their press conferences in New York City until a few days before the election, there was no time to order an ISDN. And a radio link? It is not even an option in New York City anymore, said WCBS Engineer Ed Schwartz, who received the FieldFone the day before the election and was able to use it for one of the feeds. He would have used the FieldFone for the other feed as well had another one been available. He has since bought two field units and a studio unit for such situations.
"Admittedly, it's got some limitations," said Schwartz, who tested an earlier version of the FieldFone last year with poor results. "But in our case, this is a last resort kind of thing that is infinitely better than a cell phone and better than a two-line extender."
Availability and options vary between units. To find out the delivery dates of the new Smarti and HotLine and the availability of FieldFones now in production, or to get details on options such as audio mixers, laptop computer hookup and remote contact closures, to name a few, contact your local RF Specialties representative.