Thirdly, virtually perfect mobile, portable and stationary reception will be possible, in contrast to the limitations of the VHF/FM sound broadcasting service today. In particular, receivers in automobiles and also in areas susceptible to multipath reception will be assured, unimpaired programme quality. .
Two basic digital ingredients are included in a DAB system:.
- MUSICAM (Masking Pattern Adapted Universal Sub-band Integrated Coding and Multiplexing), which is a data reduction technique,.
- COFDM (Coded Orthogonal Frequency Division Multiplexing), which is a broadband multiplexing technique, serving to enhance reception resilience in a multipath environment.
MUSICAM allows a data rate of 1441 kbit/s, necessary to deliver a stereo signal on a compact disc, to be reduced to as low as 192 kbit/s (i.e. a reduction by a factor larger than 7), for delivery of a stereo broadcast programme, the quality of which is impossible to differentiate from that of the original source. The advantage for the broadcaster is that fewer bits per second means less bandwidth is needed for transmission. .
Digital techniques allow continuous (analogue) sound signals to be converted into discrete (digital) signals. The discrete nature of these signals means that they are well-defined to within a large margin of error, thus, the signals do not loose their identity along the transmission path (under normal circumstances). Error correction methods are also available, which can further increase the "fidelity" of the transmission.
Figure 1. shows a receiver in which the wanted DAB ensemble is selected in the analogue tuner, downconverted and quadrature demodulated before applying it to an analogue- to-digital converter. Thereafter, the receiver performs the operations of the transmitter in reverse order. The digitised output of the converter is fed to the Fast Fourier Transform (FFT) stage and then differentially demodulated.