 Ofcom estimates that even after extra spectrum has been allocated to DAB , around 90 local radio stations will be unable to transmit on DAB , either because there is no space for them on a local DAB multiplex , or because they cannot afford the high transmission costs of DAB that the multiplex operators are charging . Ofcom announced in 2005 that it regarded Digital Radio Mondiale ( DRM ) as an option for local stations unable to secure carriage or unable to pay the high transmission costs of DAB . One of the drawbacks of DAB has not been addressed . In simple terms the frequency of a broadcast is the carrier frequency ( i.e. a sine wave ) In order to carry any information the carrier frequency must be modulated . The signal at the receiver ( radio ) is then demodulated and the information is retrieved . The demodulators for FM signals are almost instantaneous so that one can have radios in different areas and move between those areas to hear the broadcast continuously . In contrast the demodulators for digital signals take a finite time and each digital radio takes a different time to demodulate the broadcast signal , so that if you move between different radios that are spatially apart you are likely to hear the same part of the broadcast twice or miss parts of it depending on the time to demodulate the signal of the individual radios . The other drawback with DAB is that it is all or nothing . If there is any interference or loss due to moving out of the footprint of the broadcast signal you will receive no signal , whereas in the case of FM you can hear something even if it is crackly . 
