Sound processing method using DJ transform

A non-transitory computer-readable recording medium having recorded thereon instructions that when performed by a computer, cause the computer to:

• generate a DJ transform spectrogram indicating estimated pure-tone amplitudes for respective frequencies corresponding to natural frequencies of a plurality of springs and a plurality of time points by modeling an oscillation motion of the plurality of springs having different natural frequencies, with respect to an input sound, and calculating the estimated pure-tone amplitudes for the respective natural frequencies, wherein generating the DJ transform spectrogram includes:
• estimating expected steady-state amplitudes, each of which is a convergence value of an amplitude of each of the plurality of springs in a steady state, based on amplitudes at two time points having an interval therebetween equal to one natural period of each of the plurality of springs, and
• calculating the estimated pure-tone amplitudes based on predicted pure-tone amplitudes that are amplitudes of the input sound estimated based on the expected steady-state amplitudes;
• calculate degrees of fundamental frequency suitability based on a moving average of the estimated pure-tone amplitudes or a moving standard deviation of the estimated pure-tone amplitudes with respect to each natural frequency of the DJ transform spectrogram;
• extract the fundamental frequency based on local maximum values of the degrees of fundamental frequency suitability for the respective natural frequencies at each of the plurality of time points;
• provide, based on the fundamental frequency, a resultant frequency comprising a high measurement precision of least one of:
• (a) temporal resolution or (b) frequency resolution, and
• identify the input sound or synthesize an output sound, based on the resultant frequency.