DAB radio adds 12 new stations to UK airwaves

[peterb]

Is DAB that much of a difference to standard fm?

It can be. One of the issues is the bit rate which is variable, so Radi4 might switch to a lower bit rate (and perhaps be transmitted in mono) for a speech programme, then switch to a higher bit rate for music, to give a higher frequency response and dynamic range. Personally I don't really se that as an issue, unless the broadcaster inadvertently transmits a programme that should be at a high bit rate at a lower one.

Some audiophiles claim that the absolute quality of a digital system is inferior to that of FM, but whether the average person with average ears and average equipment can tell the difference is a moot point.

Similar arguments are made about CDs, claiming that a digital sampling system must inevitable be missing information, which ignores Shannon's sampling theory which states that provides you sample at at least twice the highest frequency, the original signal can be reproduced (which is why CDs sample at just over 44kHz, over twice the highest frequency a human ear can reliable detect at around 20 -21 kHz.

Digitisation does put a limit on dynamic range, a 12 bit sample has a dynamic range of 1: 2^24 which is 144dB, and is the limit of human hearing resolution, but in real life, say a concert hall, the dynamic range of music will be around 80dB. A compact disc samples at 16 bits, which is around 96dB. This may be enhanced with signal processing. Vinyl records also need signal processing to limit the dynamic range of the programme material to limit the physical size of the groove.

While I'm on the theme, some audio purists claim that thermionic valves give a better sound than their solid state equivalents. Of course "better" is subjective, but the design of valve amplifiers usually required a transformer in the output stage to match the high impedance output characteristic of a thermionic valve to a low load impedance presented by a loudspeaker. In a push/pull output stage, the transformer will tend to filter out even order harmonics, which the ear/brain perceive as unpleasant. Odd order harmonics do not generate the same perception.

Thermionic valves tend to have a more linear transfer characteristic at low signal levels than their transistor equivalents, however modern design teauniques and the use of FET or MOSFET output stages which have transfer characteristics similar to thermionic valves have largely negated that argument too.

[Mucka]

Nice explanation Peter