so,FM remins the best available solution... then,what 's thepoint of DAB? just selling more radio receivers?
On a technical basis, DAB (even it's original MP2 form as opposed to the more modern DAB+) is capable of delivering better sound quality that FM, especially at higher audio listening frequencies. FM audio is restricted to 15kHz at the high end of the audio range, which would give a rough equivalent of a digital sampling rate of 32kHz, whereas the MP2 & AAC audio codecs can handle a digital sampling rate of 48kHz. Though you'd have to be of a fairly young age to appreciate the difference as the higher frequency end of a person's hearing diminishes with age. For example those station playing music largely limited to the 1990's at the latest could reduce their AAC sampling rate to 32kHz and almost no one of the target audience listening would notice the high end missing - by reducing the sampling frequency means more bits can be dedicated to the portions of the audio spectrum that such people can hear! (32kHz sampling isn't allowed on original flavoured MP2 DAB, the only allowable sampling rates are IIRC 48kHz and 24kHz, the latter used for mainly speech based stations like BBC Radio 5 Live & TalkSport - though Q Radio uses it in Northern Ireland for their DAB stream with a 64kbps bitrate!)
As for DRM, it's essentially dead outside of India. Its original promotion was for LW/MW/SW bands but unless you're running "double channels" of 18-20kHz wide, the available bitrate even at lower protection levels delivered marginal audio performance levels that many whom complain about the audio quality of some DAB(+) broadcasts would go apoplectic at! Even in India, it's only All-India Radio that is pushing it in parallel with its MW broadcasts, and listening to some of its DRM broadcasts recorded off air, the quality is pretty poor.
HD Radio is the brand name for the propriety IBOC system used by some stations in North America, and is designed to be used on both the FM & MW bands. Some folks that managed to reverse engineer the system to help make it work on SDR radios found that the audio codec is a modified AAC one which gives similar results for a given bitrate.
