Radio's transition from analog to digital did not produce a single global standard. Instead, three major delivery systems now coexist: Digital Audio Broadcasting (DAB and its successor DAB+) used across Europe, Australia, and parts of Asia; HD Radio used primarily in North America; and internet streaming, which is available everywhere a data connection exists. Each system makes different engineering trade-offs between coverage, capacity, cost, and audio quality, and understanding them explains much about how radio is evolving.
DAB emerged from the European Eureka-147 research project and launched publicly in 1995, with the BBC among the first broadcasters. Rather than assigning each station its own frequency as FM does, DAB groups multiple stations into a single multiplex (an ensemble) broadcast on one frequency block, using COFDM modulation that is highly resistant to the multipath interference that plagues FM in cities. The original DAB standard used the aging MPEG-1 Audio Layer II codec, which required high bitrates for acceptable quality. The upgraded DAB+ standard, introduced in 2007, replaced it with HE-AAC v2, roughly tripling the number of stations a multiplex can carry at equivalent quality. The efficiency gain is why several countries committed fully to the platform - Norway became the first nation to switch off national FM broadcasting entirely in 2017.
HD Radio, developed by iBiquity Digital Corporation and approved by the United States Federal Communications Commission in 2002, took a different approach called in-band on-channel (IBOC). Instead of new spectrum, HD Radio embeds a digital signal in the sidebands of a station's existing AM or FM allocation. This hybrid arrangement lets a broadcaster transmit its analog signal and a digital simulcast simultaneously, plus additional digital-only subchannels (HD2, HD3). Listeners with ordinary receivers notice nothing, while HD-capable receivers decode the digital layer with improved fidelity. The design preserved existing licensing structures and receiver habits, at the cost of lower digital capacity than a dedicated DAB multiplex.
Broadcast systems and internet streaming differ most fundamentally in their scaling economics. A DAB multiplex or HD Radio signal is one-to-many: a single transmitter serves one listener or one million at identical cost, but the number of stations is capped by available spectrum. Internet streaming is one-to-one unicast: every additional listener consumes additional server bandwidth somewhere, but the number of available stations is effectively unlimited - a directory can list tens of thousands of streams from every country on Earth. Broadcast excels at mass local coverage; streaming excels at infinite choice and global reach.
Reliability and quality comparisons are more nuanced than marketing suggests. Broadcast digital radio is free to receive, drains less battery than a cellular modem, and works in coverage without any data plan - but a DAB+ station squeezed to 32 or 48 kbps HE-AAC to fit a crowded multiplex can sound worse than good FM. Internet streams face the opposite constraint: bandwidth costs money, but nothing caps quality, so stations can offer feeds from efficient 64 kbps AAC all the way to bit-perfect lossless FLAC exceeding 1,000 kbps - fidelity no broadcast standard can match. Coverage inverts the comparison: digital broadcast degrades abruptly at the edge of transmitter range, while streaming works wherever cellular or Wi-Fi does, including inside buildings, but fails in coverage gaps.
The industry's likely destination is convergence rather than victory for either side. Hybrid radio initiatives such as RadioDNS link broadcast signals with internet services, letting a car receiver tune a station over DAB+ or FM where coverage is strong and hand off seamlessly to that station's internet stream where it is not, while pulling artwork and program metadata over IP throughout. In this model, broadcast provides efficient local distribution, and the internet provides universality, interactivity, and the long tail of global stations - the listener simply hears radio, with the delivery path chosen invisibly.
References:
Hoeg, W., & Lauterbach, T. (2009). Digital Audio Broadcasting: Principles and Applications of DAB, DAB+ and DMB (3rd ed.). Wiley.
Maxson, D. (2007). The IBOC Handbook: Understanding HD Radio Technology. Focal Press.
WorldDAB (2017). Norway completes FM digital switchover. WorldDAB Forum reports.