Method and apparatus for binaural rendering audio signal using variable order filtering in frequency domain

A method for processing an audio signal, the method comprising:

• receiving an input audio signal including a plurality of subband signals, wherein the plurality of subband signals include subband signals of a first subband group having low frequencies based on a predetermined frequency band and subband signals of a second subband group having high frequencies based on the predetermined frequency band;
• receiving a set of truncated subband filter coefficients for filtering each subband signal of the plurality of subband signals, wherein the set of truncated subband filter coefficients is at least a portion of a corresponding set of subband filter coefficients obtained from binaural room impulse response (BRIR) filter coefficients for binaural filtering of the input audio signal;
• generating fast Fourier transform (FFT) filter coefficients by fast Fourier transforming each set of truncated subband filter coefficients by a block size in a corresponding subband, wherein the block size is determined to be a smaller value between a first value and a second value, wherein the first value is obtained by multiplying a reference filter length of a corresponding set of truncated subband filter coefficients by 2, and wherein the second value is a predetermined maximum FFT size;
• performing fast Fourier transform of subband signals of the first subband group based on a predetermined subframe size in the corresponding subband;
• generating at least one filtered subframe for each subband, wherein each filtered subframe is generated by multiplying a corresponding subframe and the FFT filter coefficients;
• inverse fast Fourier transforming the at least one filtered subframe for each subband;
• and
• generating a filtered subband signal by overlap-adding the at least one inverse fast Fourier transformed subframe for each subband.