A method of audio processing using a code-excited linear prediction, CELP, algorithm, the method comprising: receiving a coded audio signal comprising coding noise and a pitch; generating a decoded audio signal from the coded audio signal; determining the pitch corresponding to a fundamental frequency of the audio signal based on the decoded audio signal; characterised by determining a minimum allowable pitch for the CELP algorithm, wherein the minimum allowable pitch is a minimum pitch limit of the CELP algorithm; determining whether the pitch of the audio signal is less than the minimum allowable pitch; and applying an adaptive high pass filter on the decoded audio signal to lower the coding noise at frequencies below the fundamental frequency only when the pitch of the audio signal is less than the minimum allowable pitch, wherein a cut-off frequency of the adaptive high pass filter is less than the fundamental frequency, wherein the adaptive high pass filter is a second order high-pass filter, wherein the adaptive high pass filter is given by the F HP z = 1 + a 0 z − 1 + a 1 z − 2 1 + b 0 z − 1 + b 1 z − 2 , a 0 = − 2 ⋅ r 0 ⋅ α sm , a 1 = r 0 ⋅ r 0 ⋅ α sm ⋅ α sm , b 0 = − 2 ⋅ r 1 ⋅ α sm ⋅ cos 2 π ⋅ 0.9 F 0 _ sm , b 1 = r 1 ⋅ r 1 ⋅ α sm ⋅ α sm , wherein r o is a constant representing a largest distance between zeros and a center on a z-plane, wherein r 1 is a constant representing a largest distance between poles and the center on the z-plane, wherein Fo _sm is related to a fundamental frequency of a short pitch signal, and wherein α sm (0 ≤ α sm ≤ 1) is a controlling parameter to adaptively reduce a distance between the poles and the center on the z-plane. receiving a coded audio signal comprising coding noise and a pitch; generating a decoded audio signal from the coded audio signal; determining the pitch corresponding to a fundamental frequency of the audio signal based on the decoded audio signal; characterised by determining a minimum allowable pitch for the CELP algorithm, wherein the minimum allowable pitch is a minimum pitch limit of the CELP algorithm; determining whether the pitch of the audio signal is less than the minimum allowable pitch; and applying an adaptive high pass filter on the decoded audio signal to lower the coding noise at frequencies below the fundamental frequency only when the pitch of the audio signal is less than the minimum allowable pitch, wherein a cut-off frequency of the adaptive high pass filter is less than the fundamental frequency, wherein the adaptive high pass filter is a second order high-pass filter, wherein the adaptive high pass filter is given by the F HP z = 1 + a 0 z − 1 + a 1 z − 2 1 + b 0 z − 1 + b 1 z − 2 , a 0 = − 2 ⋅ r 0 ⋅ α sm , a 1 = r 0 ⋅ r 0 ⋅ α sm ⋅ α sm , b 0 = − 2 ⋅ r 1 ⋅ α sm ⋅ cos 2 π ⋅ 0.9 F 0 _ sm , b 1 = r 1 ⋅ r 1 ⋅ α sm ⋅ α sm , wherein r o is a constant representing a largest distance between zeros and a center on a z-plane, wherein r 1 is a constant representing a largest distance between poles and the center on the z-plane, wherein Fo _sm is related to a fundamental frequency of a short pitch signal, and wherein α sm (0 ≤ α sm ≤ 1) is a controlling parameter to adaptively reduce a distance between the poles and the center on the z-plane. <EOS>