1. An audio signal processing method comprising: generating a first target vector which is a target vector of a first stage based on a plurality of linear predictive conversion coefficients by performing linear predictive analysis on a current frame of an audio signal; acquiring a temporarily determined number of first temporary candidate code vectors of the first stage by vector-quantizing the first target vector; calculating first temporary candidate errors which are errors between the first temporary candidate code vectors and the first target vector; and determining a first number which is the number of first candidate code vectors based on the first temporary candidate errors and acquiring the same number of first final candidate code vectors as the first number.