27. An apparatus comprising: a quantizer that receives speech input signal line spectral pair frequencies, that includes at least one codebook having reference speech signal line specral pair frequencies, and that determines a distance measure between an ith speech input signal line spectral pair frequency and an ith reference speech signal line spectral pair frequency, wherein the distance measure, for i=1 to N.sub.1, is proportional to (i) a difference between the ith speech input signal line spectral pair frequency and the ith reference speech signal line spectral pair frequency and (ii) a subtraction from the difference of an ith frequency shifting factor to at least partially compensate for frequency shifting of the ith speech input signal line spectral pair frequency by acoustic noise, wherein N.sub.1 is greater that or equal to one and less than or equal to P.
35. The apparatus of claim 27 wherein the speech input signal is represented by P line spectral pair frequencies, where P is a non-negative integer, and the reference speech signal is represented by P line spectral pair frequencies.