Abstract
This analysis of the audio quality of DAB has been made independently of the broadcasting companies and aims at balancing their information.
Through measurement of the audio signal and through informal listening, we have found that DAB suffers from several problems:
• The stereo image is smeared due to heavy use of joint stereo coding. Often the stereo image lacks focus and gives incorrect localization of instruments, in certain cases there is also incorrect balance between a vocalist and the background music.
• The treble cut-off frequency is usually as low as 14 kHz and the result is a lack of brightness and a veiled sound stage. In particular young people will notice this degradation.
As young people are the target group for some of these stations, such as P3, this must be considered to be very undesirable.
The reason is that the bit rates for all the channels in the Norwegian DAB network today are much lower than what scientific evaluation of audio quality has recommended, i.e. lower than 192 - 256 kbps which was projected when DAB was debated in Stortinget (Norwegian Parliament) in 1998.
When the capacity is fully utilized, stations with music in the Oslo area use these bit rates:
• Three stations use 160 kbps with an audio quality similar to FM: P2, Alltid Klassisk1 and P4
• Twelve stations use 128 kbps with lower quality than FM, incl. P1 and P3.
• Two stations transmit in mono at rates of 80 and 96 kbps (Radio 2 Digital Moox and NRK Barn2)
It would have been desirable to stop using 128 kbps as the standard bit rate for music, and use 160 kbps instead. More demanding material should have the same quality as mp3 at 128 kbps, i.e. 192 kbps in DAB. As of today, there is not capacity to increase bit rates to these levels, so the DAB network has too low capacity with respect to requirements for decent audio quality.
The broadcast companies want us to make a choice between FM, with the best audio quality in stationary receivers, and DAB which is best in a car. Today this is an unnecessary choice as there are no technological problems in making a digital radio which is better than FM on all accounts:
• Reception without garbling in cars
• Capacity for all the stations one wants
• Audio with near-CD quality