1. An apparatus for enhancing a quantization efficiency in linear predictive encoding of a signal of speech and/or audio, the apparatus comprising: a coefficient conversion unit, implemented by a processor, configured to obtain a line spectral frequency (LSF) coefficient or an immitance spectral frequency (ISF) coefficient of a mid-subframe of the signal from a linear predictive coding (LPC) coefficient of the mid-subframe; a weighting function determination unit, implemented by a processor, configured to determine a weighting function based on a magnitude of a spectral bin corresponding to a frequency of the ISF coefficient or the LSF coefficient of the mid-subframe, wherein the weighting function is based on a maximum value of the magnitude of the spectral bin corresponding to the frequency of the ISF coefficient or the LSF coefficient and the magnitude of at least one neighboring spectral bin; and a quantization unit configured to obtain a parameter associated with the mid-subframe from a quantized ISF coefficient or a quantized LSF coefficient of a current frame and a previous frame, based on the determined weighting function of the mid-subframe.