matlab - Matlab谱图功能的手动实现
问题描述
我正在尝试实现我自己的函数,该函数给出与 Matlab 频谱图函数相同的结果。到目前为止,我已经完成了这样的功能:
function out = manulaSpectogram(x, win, noverlap, nfft)
x = x(:);
n = length(x);
wlen = length(win);
nUnique = ceil((1+nfft)/2); % number of uniqure points
L = fix((n-noverlap)/(wlen-noverlap)); % number of signal frames
out = zeros(L, nUnique);
index = 1:wlen;
for i = 0:L-1
xw = win.*x(index);
X = fft(xw, nfft);
out(i+1, :) = X(1:nUnique);
index = index + (wlen - noverlap);
end
end
在我的测试中,当参数 nfft 大于或等于窗口长度时,它可以完美运行并给出与频谱图函数相同的结果。
% first test (nnft = window length):
A = [1,2,3,4,5,6];
window = 6;
overlap = 2;
nfft = 6;
s = spectrogram(A, hamming(window), overlap, nfft)'
s2 = manulaSpectogram(A, hamming(window), overlap, nfft)
% results:
s =
9.7300 + 0.0000i -5.2936 + 0.9205i 0.7279 - 0.3737i -0.1186 + 0.0000i
s2 =
9.7300 + 0.0000i -5.2936 - 0.9205i 0.7279 + 0.3737i -0.1186 + 0.0000i
% second test (nfft > window length):
A = [1,2,3,4,5,6];
window = 3;
overlap = 2;
nfft = 6;
s = spectrogram(A, hamming(window), overlap, nfft)'
s2 = manulaSpectogram(A, hamming(window), overlap, nfft)
% results:
s =
2.3200 + 0.0000i 0.9600 + 1.9399i -1.0400 + 1.5242i -1.6800 + 0.0000i
3.4800 + 0.0000i 1.5000 + 2.8752i -1.5000 + 2.3209i -2.5200 + 0.0000i
4.6400 + 0.0000i 2.0400 + 3.8105i -1.9600 + 3.1177i -3.3600 + 0.0000i
5.8000 + 0.0000i 2.5800 + 4.7458i -2.4200 + 3.9144i -4.2000 + 0.0000i
s2 =
2.3200 + 0.0000i 0.9600 - 1.9399i -1.0400 - 1.5242i -1.6800 + 0.0000i
3.4800 + 0.0000i 1.5000 - 2.8752i -1.5000 - 2.3209i -2.5200 + 0.0000i
4.6400 + 0.0000i 2.0400 - 3.8105i -1.9600 - 3.1177i -3.3600 + 0.0000i
5.8000 + 0.0000i 2.5800 - 4.7458i -2.4200 - 3.9144i -4.2000 + 0.0000i
在窗口长度小于 nfft 的情况下,结果是不同的。
% third test (nfft < window length):
A = [1,2,3,4,5,6];
window = 6;
overlap = 2;
nfft = 3;
s = spectrogram(A, hamming(window), overlap, nfft)'
s2 = manulaSpectogram(A, hamming(window), overlap, nfft)
% results:
s =
9.7300 + 0.0000i 0.7279 - 0.3737i
s2 =
3.6121 + 0.0000i -1.6861 + 1.6807i
那么,即使在 nnft 小于窗口长度的情况下,如何改进我的功能以接收相同的结果?Matlab 的频谱图是如何计算这种情况的?
我正在尝试实现我自己的函数,因为频谱图函数是我需要从 Matlab 到 C# 语言实现的大型算法的一部分,所以我想知道频谱图“黑匣子”的作用。
解决方案
我注意到当窗口大小大于 nfft 标量时,必须以某种方式转换数据。最后我找到了一个可能在原始spectogram
Matlab 函数中调用的内部 Matlab 函数。它被命名datawrap
并包装输入数据模 nfft。
所以在我的函数中,我必须在调用 fft. 改进的功能:
function out = manulaSpectogram(x, win, noverlap, nfft)
x = x(:);
n = length(x);
wlen = length(win);
nUnique = ceil((1+nfft)/2); % number of uniqure points
L = fix((n-noverlap)/(wlen-noverlap)); % number of signal frames
out = zeros(L, nUnique);
index = 1:wlen;
for i = 0:L-1
xw = win.*x(index);
% added transformation
if length(xw) > nfft
xw = sum(buffer(xw, nfft), 2);
end
% end of added transformation
X = fft(xw, nfft);
out(i+1, :) = X(1:nUnique);
index = index + (wlen - noverlap);
end
end
spectogram
我相信它可以正常工作,因为它给出了与 Matlab函数相同的结果。
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