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DW Digital Radio DRM

Digital Versus Analog

Digital Radio Mondiale (DRM) is the name of the new standard in use for transmitting digital signals in the short-wave bands. But what does “digital” mean?

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Soon a thing of the past: Fully analog transmissions from brain (composer) to brain (listener)...

Noise-free radio programs on short, medium and long waves - that is the simple, yet precise, description of what DRM delivers. Every listener who has ever been searching for radio broadcasts in the lower bands of the frequency ranges will know how revolutionary this simple statement is.

Up to now, the reception of (analog) programs in these frequency ranges has always been highly prone to disturbances, with noise, fading and other kinds of interference reducing the audibility and listening pleasure. Digital transmissions are completely different – and that is based on the difference between analog and digital signals.

Analog oscillations

In the analog mode, the oscillations of the electric signal correspond exactly to those of the acoustic signal, whereas in the digital mode, only the information about the type of oscillation is being transmitted.

All audible sounds, be it music, language or noise, are sampled first and then "described" in form of a binary data stream, which is a sequence of high-rate unchanged electric impulses. As there are only two statuses in this data stream (“electricity flow yes” or “electricity flow no”), it is called a binary (bi = two) stream.

Free of interference

In an ideal situation, even an analog signal can be transmitted almost free of interference, but the main problem of having to filter out the disturbances still remains. With a digital signal, however, the impulses just have to correspond to a certain signal strength (be “loud enough”, so to say) to enable the receiver to separate them from any other signal and to convert the digitized sounds back to analog, i.e. the sample is re-generated according to the "description". The human ear can only detect analog signals with the sounds' oscillations having to be translated into the ear-drum's oscillations.

DRM uses the advantages offered by the AM (amplitude-modulated) technology in the ranges of short, medium and long waves (spanning large distances) and combines them with those of the digital transmission mode. A carrier frequency is modulated with digital impulses, which can be taken up by a receiver. If the signal is strong enough, the reception is clear and absolutely interference-free, but if the signal strength falls below a certain threshold value, it does not, as in case of analog transmission, fade into the noise pattern, but vanishes completely. So, there are only two alternatives for reception, i.e. “signal yes” or “signal no”. Deutsche Welle is taking this into account by extensive monitoring in order to ensure coverage as widespread as possible.

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  • Date 19.02.2009
  • Author dh
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  • Permalink http://p.dw.com/p/5VwN
  • Date 19.02.2009
  • Author dh
  • Print Print this page
  • Permalink http://p.dw.com/p/5VwN