Subjective Effects of Noise and Loss in Telephone Transmission
Tapas K. Sen · The Journal of the Acoustical Society of America · 1966
Voice transmission through telephone channels usually encounters a number of impairments that degrade the transmission quality. Two common impairments are loss of speech energy (known as “loss”) and noise. To maintain a high standard of transmission quality, it is therefore necessary to know the extent to which specific amounts of noise and loss degrade circuit quality. This paper describes an experiment concerned with this problem. 60 subjects took part in the experiment in which a range of 20 dB of loss and 40 dB of noise was used in actual telephone conversations made within the Murray Hill PBX (Bell Telephone Laboratories). The subjects' telephones were connected to a system that automatically introduced an experimental condition during calls made by the subjects. Talker volumes were measured with a volume indicator, and at the end of each call the subjects gave a rating of the transmission quality by dialing one of four predetermined digits. The results show that loss affected talker volume more significantly than noise, but influenced the ratings as significantly as noise over the range of those impairments considered.