A method of modeling characteristics of an musical instrument (21, 41) comprising a first module (503, 401), a second module (504, 402) and at least one of a prea-mplifier stage, an amplifier stage and a post amplifier stage, and exhibiting both a linear region and a non linear region (NL1, NL2), the pre-amplifier stage has a first frequency response characteristic and the post-amplifier stage has a second frequency response characteristic, characterized by comprising: feeding (S402, S403) testing input signals (Sig6, Sig7) into the musical instrument (21, 41) to obtain testing output signals (Resp6, Resp7) corresponding to the testing input signals (Sig6, Sig7), wherein the testing input signals (Sig6, Sig7) include a first testing input signal and a second testing input signal, and the testing output signals (Resp6, Resp7) include a first testing output signal (Resp6) and a second testing output signal (Resp7); identifying a breakup value (V brk) of the musical instrument (21, 41); providing the musical instrument (21, 41) with the first testing input signal based on the breakup value (V brk) and analyzing the first testing output signal (Resp6) to obtain a first profile (profile A), wherein the first testing input signal is one of a white noise signal and a chirp signal generated from a chirp filter; thus obtaining a first frequency response of the first profile (Profile A); by the second module (503, 401), providing the second testing input signal having input levels into the musical instrument (502, 41) to identify at which frequency or at which input level an output level in at least one specific frequency band of the second testing output signal (Resp7) significantly changes to produce overtones under the second testing input signal, for obtaining the second testing output signal (Resp7) having output levels and output level change rates ( m) corresponding to the input levels in at least one specific frequency band, wherein the second module analyzes the second testing output signal (Resp7); repeating all the above steps until overtone points are found in all frequencies with a frame index range so as to obtain a second profile (profile B); and by the second module (504, 402), obtaining a first frequency response characteristic of the pre-amplifier stage based on the second profile (profile B) by identifying occurrences when one of the output levels significantly changes to produce overtones and the output level change rates ( m) significantly change; modeling the characteristics based on the second profile (profile B) derived from the second output signal (Resp7), and based on the first profile, wherein the first profile (profile A) is proportional to a product of the first frequency response characteristic of the pre-amplifier stage and the second frequency response characteristic of the post-amplifier stage, and the first frequency response is divided by the first frequency response characteristic to obtain the second frequency response characteristic. feeding (S402, S403) testing input signals (Sig6, Sig7) into the musical instrument (21, 41) to obtain testing output signals (Resp6, Resp7) corresponding to the testing input signals (Sig6, Sig7), wherein the testing input signals (Sig6, Sig7) include a first testing input signal and a second testing input signal, and the testing output signals (Resp6, Resp7) include a first testing output signal (Resp6) and a second testing output signal (Resp7); identifying a breakup value (V brk) of the musical instrument (21, 41); providing the musical instrument (21, 41) with the first testing input signal based on the breakup value (V brk) and analyzing the first testing output signal (Resp6) to obtain a first profile (profile A), wherein the first testing input signal is one of a white noise signal and a chirp signal generated from a chirp filter; thus obtaining a first frequency response of the first profile (Profile A); by the second module (503, 401), providing the second testing input signal having input levels into the musical instrument (502, 41) to identify at which frequency or at which input level an output level in at least one specific frequency band of the second testing output signal (Resp7) significantly changes to produce overtones under the second testing input signal, for obtaining the second testing output signal (Resp7) having output levels and output level change rates ( m) corresponding to the input levels in at least one specific frequency band, wherein the second module analyzes the second testing output signal (Resp7); repeating all the above steps until overtone points are found in all frequencies with a frame index range so as to obtain a second profile (profile B); and by the second module (504, 402), obtaining a first frequency response characteristic of the pre-amplifier stage based on the second profile (profile B) by identifying occurrences when one of the output levels significantly changes to produce overtones and the output level change rates ( m) significantly change; modeling the characteristics based on the second profile (profile B) derived from the second output signal (Resp7), and based on the first profile, wherein the first profile (profile A) is proportional to a product of the first frequency response characteristic of the pre-amplifier stage and the second frequency response characteristic of the post-amplifier stage, and the first frequency response is divided by the first frequency response characteristic to obtain the second frequency response characteristic.