1. A digital audio encoding method comprising: (a) determining a type of a window according to a characteristic of an input audio signal; (b) generating a complex modified discrete cosine transform (CMDCT) spectrum from the input audio signal according to the determined window type; (c) generating a fast Fourier transform (FFT) spectrum from the input audio signal, by using the determined window type; and (d) performing a psychoacoustic model analysis, by using the generated CMDCT spectrum and FFT spectrum.