5. An apparatus as defined in claims 1, 2, 3 or 4 wherein said input converter means includes a means for normalizing the amplitude of the input to said lattice filter, whereby the time required to achieve a set of filter coefficients representing the input acoustic waveform is substantially independent of the amplitude of the input acoustic waveform.
5. An apparatus as defined in claims 1, 2, 3 or 4 wherein said input converter means includes a means for normalizing the amplitude of the input to said lattice filter, whereby the time required to achieve a set of filter coefficients representing the input acoustic waveform is substantially independent of the amplitude of the input acoustic waveform. 6. An apparatus as defined in claim 5 in which the amplitude normalizing means include: A. a variable gain circuit; B. means for controlling the gain of the variable gain circuit in accordance with the average amplitude of the input acoustic waveform over a predetermined length of time; and C. means for effecting a reduction in the gain of the variable gain circuit in response to an instantaneous acoustic waveform amplitude in excess of a threshold corresponding to the gain of the variable gain circuit immediately before the gain reduction.