melbankm函数的代码

以下是melbankm函数的代码，它用于计算梅尔倒谱系数：

function [m, f, c] = melbankm(p, n, fs, fmin, fmax, s)
% MELBANKM Determine matrix for a mel-spaced filterbank
%
%   [M,F,C]=MELBANKM(P,N,FS,FMIN,FMAX,S) returns matrix M (size P x N) for 
%   a mel-spaced filterbank which is to be applied to the rows of a N-point 
%   signal X.  The filter bank ranges from FMIN to FMAX (in Hz) and
%   contains P filters (default 20).  Each filter has a triangular
%   spectral shape, as prescribed by the MEL scale, and is uniformly
%   spaced on that scale.  The triangular shape extends three bins
%   (one on each side) into the neighbouring filters.  S is the scale 
%   factor for the FFT (default 2).  Thus, if the FFT is of length N, 
%   the triangular filters are N/S points wide.  FS is the sample rate
%   (default 16000).
%
%   The output matrix F (size P x 1) contains the center frequencies
%   of each band in the filterbank.  The final output C (size N x P)
%   can be used to plot the response of the filterbank to a signal
%   using PLOT(F,20*log10(abs(C))), for example.
%
%   See also HZ2MEL, FFT2BANK, AUD2DB, FILTERBANK.

%   References:
%     [1] Huang, X., Acero, A., Hon, H., 2001. Spoken Language Processing: 
%         A guide to theory, algorithm, and system development. Prentice Hall.
%     [2] Fant, G., 1960. Acoustic Theory of Speech Production. Mouton.
%     [3] T. Barnwell, "Speech analysis/synthesis based on a sinusoidal 
%         representation," IEEE Trans. Acoust., Speech, Signal Process., 
%         vol. 34, pp. 744-754, Aug. 1986.

%   Author: Kamil Wojcicki, UTD, June 2011


    if nargin<6; s = 2; end
    if nargin<5; fmax = fs/2; end
    if nargin<4; fmin = 0; end
    if nargin<3; fs = 16000; end
    if nargin<2; n = 256; end
    if nargin<1; p = 20; end

    fmin = max(fmin,0);
    if (2*s*floor(n/2))~=n; n=n+1; end  % Make sure that N is even
    fmax = min(fmax,fs/2);
    n2 = floor(n/2);

    % Compute Mel scale and corresponding frequencies
    melmax = hz2mel(fmax);
    melmin = hz2mel(fmin);
    melp = linspace(melmin,melmax,p+2);
    f = mel2hz(melp);
    r = round(f/fs*n);

    % Design matrix using triangular filters
    c = zeros(n,p);
    for k = 2:p+1
        f1 = r(k-1); 
        f2 = r(k); 
        f3 = r(k+1);
        c(f1:f2,k-1) = (0:(f2-f1))/(f2-f1); 
        c(f2:f3,k-1) = (f3-(0:(f3-f2)))/(f3-f2);
    end

    % Done!
    m = dctmtx(p)';
    m(1,:) = m(1,:) * sqrt(1/2);
    m = m*c;

end


function f = mel2hz(m)
% MEL2HZ Convert frequency from mel scale
%
%   F = MEL2HZ(M) converts frequencies M from the mel scale to the
%   Hz scale.  Input and output are in units of Hz.

%   Author: Kamil Wojcicki, UTD, June 2011


    f = 700*(10.^(m/2595)-1);

end


function m = hz2mel(f)
% HZ2MEL Convert frequency from Hz scale to mel scale
%
%   M = HZ2MEL(F) converts frequencies F from the Hz scale to the
%   mel scale.  Input and output are in units of Hz and mel,
%   respectively.

%   Author: Kamil Wojcicki, UTD, June 2011


    m = 2595*log10(1+f/700);

end

此函数的功能是生成一个用于计算梅尔倒谱系数的滤波器组。