谱减法（二）

由于第一种谱减法中存在音乐噪声难以去除，故利用过减法来进一步去除噪声。

    #subtract the noise power from the noisy power   
    #use over_subtraction method to enhance the signal
    alpha = 4
    gamma = 1
    beta = 0.0001

    power_enhanc = np.power(power_noisy, gamma) - alpha * np.power(power_noise, gamma)
    power_enhanc = np.power(power_enhanc, 1/gamma)
    #use beta*power_noise to instead of small negative values
    mask = (power_enhanc >= beta * power_noise) - 0
    print(mask.shape)
    power_enhanc = mask * power_enhanc + (1-mask) * beta * power_noise
    Mag_enhanc = np.sqrt(power_enhanc)

主要实现如图所示

由于过减，造成其谱线不连续，所以要进行平滑机制

最大噪声残差

    ## introduce the smoothing method to enhance the signal
    Mag_noisy_new = np.copy(Mag_noisy)
    k = 1
    for t in range(k,T-k):
        Mag_noisy_new[:,t] = np.mean(Mag_noisy[:,t-k:t+k+1], axis=1)

    power_noisy = Mag_noisy_new**2

 # compute the max
    Mag_enhanc_new = np.copy(Mag_enhanc)
    maxnr = np.max(np.abs(noisy_stft[:,:31])-Mag_noise,axis = 1)
    k = 1
    for t in range(k,T-k):
        index =np.where(Mag_enhanc[:,t] < maxnr)[0]
        temp =np.min(Mag_enhanc[:,t-k:t+k+1], axis=1)
        Mag_enhanc_new[index,t] = temp[index]
        enhanc_stft = Mag_enhanc_new * np.exp(1j*Phase_noisy)
    enhanc = librosa.istft(enhanc_stft, hop_length=128,win_length=256)
    sf.write("enhanc3.wav", enhanc, fs)
    print(fs)

降噪效果得到明显改善