14. An apparatus for recognizing particular phonemes in a voice signal as in claim 13, further comprising log circuit means for calculating the logarithms of said respective average power levels and said respective power levels, and wherein said first difference levels represent the differences between said respective logarithms, whereby the influence on said first difference levels of variations in emphasis from phoneme to phoneme of a particular speaker is minimized.
15. An apparatus for recognizing particular phonemes in a voice signal as in claim 14, wherein said log circuit means includes bias means for applying a bias to each said average power level and to each said power level prior to calculating the logarithms thereof, whereby the influence on said first difference levels of extraneous noise during silences in said voice signal is minimized.