Audio quality level vs. signal-to-interference ratio in isofrequency {FM} broadcasting

Frequency modulated (FM) transmissions play a key role into radio broadcasting. This paper presents a study on the audio quality of demodulated FM transmissions corrupted by co-channel interference. A panel of listeners has judged audio signals containing the superposition of "desired" and "interfering" signals with different signal-to-interference ratios (SIR). The paper summarises the outcomes of a comprehensive campaign of audio tests, which provide detailed estimates of the perceived quality of interfered FM transmissions. Furthermore, the paper presents a thorough analysis and interpretation of the tests, which establishes a relationship between five-grade ITU-R BS.1284-2 QoS scale and signal-to-interference ratio (SIR).