Perceived audio quality of realistic FM and DAB+ radio broadcasting systems

The perceived audio quality of a digital broadcasting system such as DAB+ is dependent on what type of coding and bit rates are applied. Due to bandwidth constraints, audio quality is prone to be in conflict with other service demands such as the number of channels and the transfer of ancillary data. Compared to DAB+, several other audio services have superior bit rates that challenge the audio quality of DAB+. This paper reviews audio-quality criteria and investigates how the perceived audio quality of different broadcasting systems complies with the criteria. Two studies were conducted: Test 1 where DAB+ codecs were tested at bit rates between 96 and 192 kbit/s and Test 2 where DAB+ systems between 48 and 192 kbit/s as well as FM systems were tested. The systems in Test 2 were designed to as far as possible model a realistic broadcasting signal chain including commonly used dynamic processors. The studies were realized through two listening experiments using the ITU-R recommendations BS.1116 and BS.1534 (MUSHRA) followed by a closing interview. The results showed that the currently highest available subchannel bit rate for DAB+ (192 kbit/s) was insufficient for attaining perceptually transparent quality for critical items, whereas it enabled a quality comparable to or in some instances better than a modern FM system. Extrapolation of data indicates that critical items may need to be coded at even higher bit rates to reach perceptually transparent quality. From the interviews, auditory features important for the subjects’ assessment of quality were observed. This study concludes that when making decisions on broadcasting systems, it is important to have well-founded and clearly defined criteria for minimum acceptable quality and/or perceptually transparent quality.Validerad; 2013; 20131115 (johsod)