梅尔倒谱系数（MFCC）实现

技术  /  管理员 发布于 7年前   176

本文实例为大家分享了梅尔倒谱系数实现代码，供大家参考，具体内容如下

""" @author: zoutai@file: mymfcc.py @time: 2018/03/26 @description:"""from matplotlib.colors import BoundaryNormimport librosaimport librosa.displayimport numpyimport scipy.io.wavfilefrom scipy.fftpack import dctimport matplotlib.pyplot as pltimport numpy as np# 第一步-读取音频，画出时域图（采样率-幅度）sample_rate, signal = scipy.io.wavfile.read('OSR_us_000_0010_8k.wav') # File assumed to be in the same directorysignal = signal[0:int(3.5 * sample_rate)]# plot the wavetime = np.arange(0,len(signal))*(1.0 / sample_rate)# plt.plot(time,signal)plt.xlabel("Time(s)")plt.ylabel("Amplitude")plt.title("Signal in the Time Domain ")plt.grid('on')#标尺，on：有，off:无。# 第二步-预加重# 消除高频信号。因为高频信号往往都是相似的，# 通过前后时间相减，就可以近乎抹去高频信号，留下低频信号。# 原理：y(t)=x(t)−αx(t−1)pre_emphasis = 0.97emphasized_signal = numpy.append(signal[0], signal[1:] - pre_emphasis * signal[:-1])time = np.arange(0,len(emphasized_signal))*(1.0 / sample_rate)# plt.plot(time,emphasized_signal)# plt.xlabel("Time(s)")# plt.ylabel("Amplitude")# plt.title("Signal in the Time Domain after Pre-Emphasis")# plt.grid('on')#标尺，on：有，off:无。# 第三步、取帧，用帧表示frame_size = 0.025 # 帧长frame_stride = 0.01 # 步长# frame_length-一帧对应的采样数, frame_step-一个步长对应的采样数frame_length, frame_step = frame_size * sample_rate, frame_stride * sample_rate # Convert from seconds to samplessignal_length = len(emphasized_signal) # 总的采样数frame_length = int(round(frame_length))frame_step = int(round(frame_step))# 总帧数num_frames = int(numpy.ceil(float(numpy.abs(signal_length - frame_length)) / frame_step)) # Make sure that we have at least 1 framepad_signal_length = num_frames * frame_step + frame_lengthz = numpy.zeros((pad_signal_length - signal_length))pad_signal = numpy.append(emphasized_signal, z) # Pad Signal to make sure that all frames have equal number of samples without truncating any samples from the original signal# Construct an array by repeating A（200） the number of times given by reps（348）.# 这个写法太妙了。目的：用矩阵来表示帧的次数，348*200，348-总的帧数，200-每一帧的采样数# 第一帧采样为0、1、2...200;第二帧为80、81、81...280..依次类推indices = numpy.tile(numpy.arange(0, frame_length), (num_frames, 1)) + numpy.tile(numpy.arange(0, num_frames * frame_step, frame_step), (frame_length, 1)).Tframes = pad_signal[indices.astype(numpy.int32, copy=False)] # Copy of the array indices# frame：348*200，横坐标348为帧数，即时间；纵坐标200为一帧的200毫秒时间，内部数值代表信号幅度# plt.matshow(frames, cmap='hot')# plt.colorbar()# plt.figure()# plt.pcolormesh(frames)# 第四步、加汉明窗# 傅里叶变换默认操作的时间段内前后端点是连续的，即整个时间段刚好是一个周期，# 但是，显示却不是这样的。所以，当这种情况出现时，仍然采用FFT操作时，# 就会将单一频率周期信号认作成多个不同的频率信号的叠加，而不是原始频率，这样就差生了频谱泄漏问题frames *= numpy.hamming(frame_length) # 相乘，和卷积类似# # frames *= 0.54 - 0.46 * numpy.cos((2 * numpy.pi * n) / (frame_length - 1)) # Explicit Implementation **# plt.pcolormesh(frames)# 第五步-傅里叶变换频谱和能量谱# _raw_fft扫窗重叠，将348*200，扩展成348*512NFFT = 512mag_frames = numpy.absolute(numpy.fft.rfft(frames, NFFT)) # Magnitude of the FFTpow_frames = ((1.0 / NFFT) * ((mag_frames) ** 2)) # Power Spectrum# plt.pcolormesh(mag_frames)## plt.pcolormesh(pow_frames)# 第六步，Filter Banks滤波器组# 公式：m=2595*log10(1+f/700)；f=700(10^(m/2595)−1)nfilt = 40 #窗的数目low_freq_mel = 0high_freq_mel = (2595 * numpy.log10(1 + (sample_rate / 2) / 700)) # Convert Hz to Melmel_points = numpy.linspace(low_freq_mel, high_freq_mel, nfilt + 2) # Equally spaced in Mel scalehz_points = (700 * (10**(mel_points / 2595) - 1)) # Convert Mel to Hzbin = numpy.floor((NFFT + 1) * hz_points / sample_rate)fbank = numpy.zeros((nfilt, int(numpy.floor(NFFT / 2 + 1))))for m in range(1, nfilt + 1): f_m_minus = int(bin[m - 1]) # left f_m = int(bin[m])  # center f_m_plus = int(bin[m + 1]) # right for k in range(f_m_minus, f_m): fbank[m - 1, k] = (k - bin[m - 1]) / (bin[m] - bin[m - 1]) for k in range(f_m, f_m_plus): fbank[m - 1, k] = (bin[m + 1] - k) / (bin[m + 1] - bin[m])filter_banks = numpy.dot(pow_frames, fbank.T)filter_banks = numpy.where(filter_banks == 0, numpy.finfo(float).eps, filter_banks) # Numerical Stabilityfilter_banks = 20 * numpy.log10(filter_banks) # dB;348*26# plt.subplot(111)# plt.pcolormesh(filter_banks.T)# plt.grid('on')# plt.ylabel('Frequency [Hz]')# plt.xlabel('Time [sec]')# plt.show()## 第七步，梅尔频谱倒谱系数-MFCCsnum_ceps = 12 #取12个系数cep_lifter=22 #倒谱的升个数？？mfcc = dct(filter_banks, type=2, axis=1, norm='ortho')[:, 1 : (num_ceps + 1)] # Keep 2-13(nframes, ncoeff) = mfcc.shapen = numpy.arange(ncoeff)lift = 1 + (cep_lifter / 2) * numpy.sin(numpy.pi * n / cep_lifter)mfcc *= lift #*# plt.pcolormesh(mfcc.T)# plt.ylabel('Frequency [Hz]')# plt.xlabel('Time [sec]')# 第八步，均值化优化# to balance the spectrum and improve the Signal-to-Noise (SNR), we can simply subtract the mean of each coefficient from all frames.filter_banks -= (numpy.mean(filter_banks, axis=0) + 1e-8)mfcc -= (numpy.mean(mfcc, axis=0) + 1e-8)# plt.subplot(111)# plt.pcolormesh(mfcc.T)# plt.ylabel('Frequency [Hz]')# plt.xlabel('Time [sec]')# plt.show()# 直接频谱分析# plot the wave# plt.specgram(signal,Fs = sample_rate, scale_by_freq = True, sides = 'default')# plt.ylabel('Frequency(Hz)')# plt.xlabel('Time(s)')# plt.show()plt.figure(figsize=(10, 4))mfccs = librosa.feature.melspectrogram(signal,sr=8000,n_fft=512,n_mels=40)librosa.display.specshow(mfccs, x_axis='time')plt.colorbar()plt.title('MFCC')plt.tight_layout()plt.show()

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