如何創建在MFCC中用於MATLAB中語音識別的三角形（Mel）濾鏡庫？

Question

盡管可能有內置的功能可用，但我需要創建自己的三角濾波器組。 下面是我的代碼。 我在HMatrix（filterbank）中得到NaN值。 這是由於創建矩陣時使用的FreqArray中的“相同”值所致。 我在以下問題上需要幫助：

1. 知道我選擇的44100Hz采樣頻率是否正確嗎？
2. 如何選擇較低的頻率= 300Hz和較高的頻率= 8000Hz來計算梅爾濾波器組矩陣？
3. 如何選擇合適的幀大小（frame_length）和梅爾濾波器的數量（no_of_coeffs）？

function TriFilterBank()
tic
%-----------------------------INITIALISATION---------------------------%


fs=44100; %frequency at which I have sampled my recorded samples
frame_length=256; %How to choose an appropriate frame-size?
low_freq=300; %lower frequency for calculation of mel frequency filter bank (I'm unable to choose a correct one, and find the criteria for choosing it)
high_freq=8000; %upper frequency for calculation of mel frequency filter bank (I'm unable to choose a correct one, and find the criteria for choosing it)
                % I have also tried with (fs/2)=22050Hz, but nno good results 
no_of_coeffs=20;    % This is no. of Mel-Filter banks to create. how to choose a approriate value for this for speech processing applications?


%--------------------------------------------------PRE-PROCESSING FOR MEL FILTER BANK CREATION-----------------------------------------------%

low_linear=2595*log10(1+(low_freq/700));
high_linear=2595*log10(1+(high_freq/700));
band_length=(high_linear-low_linear)/(no_of_coeffs+1); 

MelArray(no_of_coeffs+2,1)=zeros(); %to store mel frequencies to calculate mel frequency filter bank
LinearArray(no_of_coeffs+2,1)=zeros();  %to store linear frequencies to calculate mel frequency filter bank
FreqArray(no_of_coeffs+2,1)=zeros();    %to store frequency array to calculate mel frequency filter bank
%{
THIS ARRAY MAY HAVE WRONG VALUES DUE TO SELECTION of WRONG PARAMETERS LIKE low_freq, high_freq, frame_length (frame-size), no_of_coeffs (no. of filter banks). THIS IS MAJOR REASON BEHIND GENERATION OF NaN values in HMatrix
%} 
HMatrix(no_of_coeffs,frame_length)=zeros();  %Hmk Matrix/ Filter Bank I'M VERY DOUBTFUL OF THE VALUES GENERATED BY THIS FILTER BANK

MelArray(1)=low_linear;
MelArray(no_of_coeffs+2)=high_linear;
LinearArray(1)=low_freq;
LinearArray(no_of_coeffs+2)=high_freq;
FreqArray(1)=floor((int32(frame_length)+1)*LinearArray(1)/fs);
FreqArray(no_of_coeffs+2)=floor((int32(frame_length)+1)*LinearArray(no_of_coeffs+2)/fs);



for m=1:no_of_coeffs
    MelArray(m+1)=MelArray(m)+band_length;
    LinearArray(m+1)=700*((power( 10,MelArray(m+1)/2595))-1);
    FreqArray(m+1)=floor((int32(frame_length)+1)*LinearArray(m+1)/fs); %The values generated here seem to be doubtful, hence maybe an incorrect filter bank
end


% THE MOST DOUBTFUL/WRONG PART i.e. MEL FREQUENCY FILTER BANK MATRIX CREATION

%---------------------------------------------------------PROBABLE ERRONEOUS PART------------------------------------------------------------%
% I'M GETTING NaN values in this matrix probably due to choosing incorrect parameters for  like upper freq, lower freq, frame-size, no.of filter banks, sampling frequency etc.
% In FreqArray I'm getting two same values, hence it's satisfying none of the below conditions and generating a NaN value.

for k=1:frame_length
    for m=1:no_of_coeffs
        if(k<FreqArray(m))
            HMatrix(m,k)=0;
        elseif (FreqArray(m)<=k && k<=FreqArray(m+1))
            HMatrix(m,k)=(k-FreqArray(m))/(FreqArray(m+1)-FreqArray(m));
        elseif(FreqArray(m+1)<=k && k<=FreqArray(m+2))
             HMatrix(m,k)=(FreqArray(m+2)-k)/(FreqArray(m+2)-FreqArray(m+1));
        elseif (k>FreqArray(m+2))
             HMatrix(m,k)=0;
        end
    end
end
%--------------------------------------------------------------------------------------------------------------------------------------------%
save('TriFilterBank');
toc    
end

該代碼基於以下等式：

上面的代碼輸出的主要部分如下所示，以供參考。

作為參考，我使用了以下網站：

http://practicalcryptography.com/miscellaneous/machine-learning/guide-mel-frequency-cepstral-coefficients-mfccs/

提前致謝！

Answer 1

知道我選擇的44100Hz采樣頻率是否正確嗎？

這個頻率很好。 無論如何，語音駐留在16khz以下，因此16kHz是更常見的選擇。 在您用作參考的博客文章中，它是16kHz。

如何選擇較低的頻率= 300Hz和較高的頻率= 8000Hz來計算梅爾濾波器組矩陣？

此范圍不是最佳范圍，但對於大多數應用程序來說還可以。 為了獲得高質量的聲音，范圍為20Hz至7600Hz。

如何選擇合適的幀大小（frame_length）和梅爾濾波器的數量（no_of_coeffs）？

語音的幀大小通常約為25毫秒，這是在一幀內提供平穩性和正常速率語音分辨率的最佳值。 對於44100 kHz的采樣率，它以幀中的大約1128（44100 * 0.025）個元素結束，而不是您選擇的256個元素。 如果要具有2的冪，則一幀中需要2048個元素。 這也將是FFT階數。

梅爾過濾器的數量可以是15-40，在許多系統中使用20是一個很好的值，發現它在實驗中很有用。

最好閱讀現有的實現，有許多您從本教程中學不到的東西，其中一個很好的是VoiceBox 。