An audio signal processing method comprising: acquiring a plurality of frequency-converted coefficients by performing frequency conversion with respect to an audio signal; the method being further characterised by: selecting one of a generic mode and a non-generic mode based on a pulse ratio with respect to frequency-converted coefficients of a high frequency band among the plurality of frequency-converted coefficients; and if the non-generic mode is selected, performing the following steps of: extracting a predetermined number of pulses from the frequency-converted coefficients of the high frequency band and generating pulse information; generating an original noise signal excluding the pulses from the frequency-converted coefficients of the high frequency band; generating a reference noise signal using frequency-converted coefficients of a low frequency band among the plurality of frequency-converted coefficients; and generating noise position information and noise energy information using the original noise signal and the reference noise signal, wherein the pulse ratio is a ratio of energy of a plurality of pulses to total energy of a current frame, wherein the pulse information includes at least one of pulse position information, pulse sign information, pulse amplitude information and pulse sub-band information, wherein the noise position information indicates a start position of sub-band in which similarity between the original noise signal and the reference noise signal has a best value. acquiring a plurality of frequency-converted coefficients by performing frequency conversion with respect to an audio signal; the method being further characterised by: selecting one of a generic mode and a non-generic mode based on a pulse ratio with respect to frequency-converted coefficients of a high frequency band among the plurality of frequency-converted coefficients; and selecting one of a generic mode and a non-generic mode based on a pulse ratio with respect to frequency-converted coefficients of a high frequency band among the plurality of frequency-converted coefficients; and if the non-generic mode is selected, performing the following steps of: extracting a predetermined number of pulses from the frequency-converted coefficients of the high frequency band and generating pulse information; generating an original noise signal excluding the pulses from the frequency-converted coefficients of the high frequency band; generating a reference noise signal using frequency-converted coefficients of a low frequency band among the plurality of frequency-converted coefficients; and generating noise position information and noise energy information using the original noise signal and the reference noise signal, extracting a predetermined number of pulses from the frequency-converted coefficients of the high frequency band and generating pulse information; generating an original noise signal excluding the pulses from the frequency-converted coefficients of the high frequency band; generating a reference noise signal using frequency-converted coefficients of a low frequency band among the plurality of frequency-converted coefficients; and generating noise position information and noise energy information using the original noise signal and the reference noise signal,