Equivalent Peak Level: A Threshold-Independent Speech-Level Measure

Previous research showed that the logarithm of the absolute voltage of a speech waveform is nearly uniformly distributed between same arbitrary threshold and a peak. In the present study, the equivalent peak level (epl) of a speech sample is defined as that peak of a log-uniformly distributed random variable that would have produced the same rms above threshold as was measured from the speech sample. Measurements on 116 speech samples show that if threshold is varied over a range of at least 35 dB on repeated measurements of the same speech sample, the epl varies ±1 dB. Equivalently, if the measuring threshold is held constant, the epl will follow known speech level changes on a decibel-for-decibel basis to within ±1 dB over a 35-dB range. The epl may be measured with any facility having means of obtaining rms-above-threshold.