A Laboratory System for Measuring Loudness Loss of Telephone Connections
Joseph L. Sullivan · Bell System Technical Journal · 1971
Transmission performance of the telephone message network has improved steadily over the years. Coincidental with this improvement has been the evolution of rating plans which provide the basis for transmission planning, design, and evaluation. Loudness of telephone speech was an important consideration in this evolution. Telephone speech loudness continues to be one of the major factors which need to be taken into account in telephone transmission engineering. This paper covers a laboratory system, called EARS (Electro-Acoustic Rating System), devised to make objective measurements of partial and overall telephone connections (including electro-acoustic transducer efficiencies) in a manner which reflects subjective loudness loss. Topics covered include a historical review of rating plans, computation of speech loudness, evolution of the EARS, and description of the system and its capabilities. The EARS essentially comprises a sound source and a meter for measuring either acoustical pressure or electrical voltage. Design of the source and meter are based on telephone speech loudness considerations, and measurements made with the system approximate subjective loudness judgments with an accuracy which is sufficient for telephone engineering purposes. The EARS may be used in implementing any telephone transmission rating plan incorporating speech loudness loss as an element. In such application, the system can be used for specifying connection losses, thus eliminating the need for extensive subjective tests of loudness. However, subjective tests will still be required to evaluate effects of other elements, e.g., noise, important in any given plan, and to evaluate the range of loudness losses acceptable for that plan.