AUDIO QUALITY ON THE AIR IN DAB DIGITAL RADIO IN NORWAY
Sverre Holm · 2007
The same program heard on DAB at 128 kbit/s and 192 kbit/s has been compared with a high quality FM stereo signal. The result from informal listening tests is that there are audible impairments in the stereo imaging of high-frequency instruments, and in particular hi-hats at 128 kbit/s. Some examples of songs where this effect can be heard are given. The effect can be explained by spectral analysis of the output of a DAB radio which shows that at 128 kbit/s, 3 kHz is used as the switch frequency for the intensity stereo coding of the MPEG-I layer 2 encoder, effectively removing most signal differences above this frequency. This degradation cannot be heard in a good quality FM stereo signal.