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.
8. A method as described in claim 6, wherein said finding of the difference between the energy of a given spectral parameter and a spectral parameter in a nearby frame further includes: finding a third difference between the energy of said given spectral parameter of said given frame and the energy, in a certain nearby frame, of a spectral parameter associated with a frequency band which is above the frequency band of the given parameter by an amount Y, which is larger than X; and finding a fourth difference between the energy of said given spectral parameter and the energy, in another 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 Y, where said another nearby frame is on the opposite side of said given frames as said certain nearby frame; and said using of a difference to calculate a slope parameter includes combining the negative of one of said third and fourth differences to the value of the other of those two differences to form a second net difference which is also used to calculate said slope parameter.