1. A method of speech analysis comprising: representing a length of speech as a temporal sequence of frames, with each frame representing speech sounds at one of a succession of brief time periods; analyzing each frame of speech to obtain a plurality of spectral parameters, each of which represents the energy at one of a series of different frequency bands; finding the difference between the energy of a given spectral parameter of a given frame and the energy, in a nearby frame, of a spectral parameter associated with an energy band which is close to, but different than, the frequency band represented by said given spectral parameter; and using that difference to calculate a slope parameter which provides an indication of the extent to which the frequency of the acoustic energy in the part of the spectrum represented by said given spectral parameter is going up or going down.
6. A method as described in claim 1, wherein: said finding of the difference between the energy of a given spectral parameter and a spectral parameter in a nearby frame includes: finding a first difference between the energy of said given spectral parameter of said given frame and the energy, in a first nearby frame, of a spectral parameter associated with an frequency band which is above the frequency band of the given parameter by an amount X; and finding a second difference between the energy of said given spectral parameter and the energy, in a second nearby frame, of a spectral parameter associated with a frequency band which is below the frequency band of the given parameter by approximately an amount X, where said second nearby frame is on the opposite side of said given frame as said first nearby frame; and said using of a difference to calculate a slope parameter includes combining the negative of the value of one of said first and second differences to the value of the other of said differences to form a first net difference which is used to calculate said slope parameter.