Fresh off the heels of the FCC's veritable rubber-stamping of the "HD" digital radio protocol, the broadcasters behind iBiquity's technology are wasting no time in preparing to lock down its content. Think about this the next time an NAB executive testifies on Capitol Hill and proclaims the virtue of so-called "free" over-the-air radio.

NDS, a maker of digital media encryption technology, recently signed a deal with iBiquity to provide HD Radio with an encrypted content-delivery system that effectively institutes subscriptions capability on digital radio.

"RadioGuard" is derived from NDS' "VideoGuard" technology, which it claims will allow radio stations to provide "more choices to their listeners, a broader selection of content and more segmentation opportunities for advertisers, all of which provide additional revenue-generating possibilities."

"Consumers," says NDS, "will be able to take advantage of services not currently offered in today’s terrestrial or satellite radio environments. These services include pay-per-listen options for live concerts and events, improved radio reading services for the blind, private channels for emergency operators, and opt-in events sponsored by advertisers." It should be noted that some of these, such as radio reading services for the blind, are already offered for free, provided the listener purchases a special receiver designed to separate unencrypted subcarrier signals from analog FM broadcasts.

Given that there's such extremely limited bandwidth available in the HD Radio environment - about 140 kilohertz in the FM "extended hybrid" analog/digital configuration - it's difficult to see how stations would continue to multicast multiple free streams of program content while also offering up something for those willing to pay for it. Something will have to give; data compression solutions only go so far.

Of course, terrestrial radio needs to come up with program content that's worth paying for. But that's beside the point. Up until now, all AM and FM radio was free - you just paid for the cost of the receiver, though digital ones still cost in the three-figure range, and those currently being sold will not be compatible with NDS' "conditional access" technology.

Now, perhaps, we will witness the beginning of the fencing-off what used to be fully public spectrum, for purposes that only serve a public willing to pay. Terrestrial radio's never been set up like that. The same thing has already happened with DTV, though, so I guess its coming should be no real surprise.

Although the FCC has not formally ruled on exactly how digital broadcasters may split their spectrum up into free and pay-for-play services, this deal is obviously a move by iBiquity to implement the capability in order to set the ground work for official endorsement. After all, that is essentially how HD Radio itself was developed and deployed.

However, unlike DTV, the proprietary nature of the fundamental HD broadcast standard has knock-on effects with regard to the features the standard will allow. iBiquity is thus in a position to define the range of add-on features available in the digital environment, like "conditional access" services. In this case, if you want to offer subscription-only content on terrestrial radio, you'll have to go through RadioGuard - no alternate protocols allowed.

In this light, this latest development shouldn't be heralded as a great leap forward for digital broadcast technology, but as another step in the direction of conditioning the public to pay for a medium that has historically been free.