Statistical Basis for Objective Measurement of Speech Levels
Paul T. Brady · The Journal of the Acoustical Society of America · 1965
First-order probability distributions of speech amplitudes are studied to obtain a suitable 1-dimensional measure of speech level. The logarithm of the level of the long-term syllabic waveform is found to be approximately uniformly distributed above a threshold. The average peak level (APL) is obtained by taking the time average of the log of the syllabic waveform and deriving from it the peak of the log-uniform distribution that would have produced the same average. It is shown that changes in the over-all speech level are ideally more linearly reflected by the APL than by certain other level indicators, such as root mean square or average voltages. The digital speech-level meter is described as an instrumentation of the technique used to obtain the APL. Measurements made with this meter are easily obtained and very repeatable. Although the results so far are promising, much work is yet needed to fully determine the applications of the device.