Signal-to-noise ratio and aural assessment of broadcast reception quality

Historically, radiotelephony speech intelligibility has been equated to signal-to-noise ratio (SNR). Although the human being has proven to be a reasonably consistent measurement system for determining voice quality delivered by various radio systems, assembling listening panels can prove to be troublesome. Consequently, most voice intelligibility experiments are now conducted using pre-set SNRs which can be equated to a specified articulation score or level of intelligibility. A major exception is the HF broadcast community which continues to use humans to monitor reception quality in the coverage area. As more broadcasters use HF propagation prediction programs to plan operations, a relationship between monitor scores of broadcast quality and the equivalent SNR is desired. A procedure for adjusting laboratory measurements to standards for HF radio reception of voice transmissions was developed by Silva (1945, 1946) and further advanced by Akima et al. (1969). The paper presents an adaptation of these earlier works for use in predicting the quality of HF broadcast coverage. The efficacy of this model is tested using data acquired from VOA radio monitors. The results of the comparison show that predictions can be used to extrapolate monitor reports to area coverage. The prediction model used in the study is the VOACAP