Digital audio broadcasting (DAB) was initiated in the 1980s, launched in the UK in 1995 and is becoming increasingly popular. That’s due to the improved quality of the service when compared to analogue and its greater efficiency giving it the ability to offer more radio services in the same amount of bandwidth.
Analogue and DAB Radio Transmission Methods
The principle behind radio is that a device transmits a form of electrical energy that is picked up wirelessly by a receiver using an aerial. The transmitted energy spreads out as radio waves that are characterised by their frequency measured in hertz that can number several million per second.
Each analogue radio station transmission is at a different frequency, enabling a radio receiver to tune into and identify a particular station.
A process known as modulation attaches a radio programme to a carrier radio wave. This can be by one of two processes:
- Amplitude modulation (AM, otherwise known as medium wave or MW), where the size of the carrier wave’s peak is adjusted
- Frequency modulation (FM), where the carrier wave’s frequency is different.
Rather than sending signals based on the length or frequency of the carrier wave, DAB works digitally by sending a series of numbers, coded in digital format as a string of zeroes and ones. In this case, the signals for radio programme are split into fragments and given coded digits, which are then compressed and transmitted many times so at least some are more likely to be received.
The DAB radio receiver collects the unique radio signals, expands and reassembles the fragments then recreates the programme being broadcast. Because it has to do so much processing, what you hear on a DAB radio will lag slightly behind an analogue version.
Advantages of DAB Radio
Each digital radio signal is transmitted across an extremely wide band, which has several advantages:
- The width of the band enables different streams of data to be carried on one digital signal, a process known as multiplexing. Typically, a signal might contain a music track and text information about it (the radio station, current programme, name of the track and artists) which can be displayed on the radio.
- Because the signal is so wide, it can bypass obstacles and still get through to the radio receiver. This means you will get better reproduction of the sound and won’t lose service in the same way as for analogue if your car goes under a bridge or enters a tunnel, for example.
Being a more modern technology, DAB delivers a purer signal with less noise. The signal also degrades quickly as the signal fades when the transmitter becomes out of range rather than becoming poorer in quality, like analogue.
Digital radio doesn’t use frequencies, as analogue does, so there is no audio interference. It also discards sounds that cannot be heard and so only broadcasts the essential information. The signal carries an in-built protection system to prevent transmission errors.
Although DAB radios are increasingly available and have superseded the analogue versions, there’s no immediate need to replace your old set. Radio stations continue to broadcast programmes in analogue form alongside the digital transmissions.
That gives you the chance to compare the relative quality of the two methods, with digital radio from FM stations reckoned to be the equivalent of CD quality while AM stations have the superior FM quality when received digitally. It also lets you experience the time lag that the additional digital processing creates.