Matlab谱图、黄油和滤波函数问题

Question

1. 我如何改变光谱图的颜色，以显示更强烈的接近紫色，而不那么强烈接近红色？
2. 如何将黄油和过滤器功能应用于wav文件以显示：

- a lowpass cutting frecuency of 4500hz
- a bandstop with central fecruency of 3000 hz and bandwith of 1000 hz

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然后在光谱中显示这些过滤过的信号？

Answer 1

下面的Matlab代码应该能做你想做的事情。过滤器设计的参数被定义为变量，可以更改以调整过滤器。如果你想把情节分开，只需删除subplot(3,1,x)，把figure放在spectrogram之前。那你就有三个单独的地块了。

若要使用.wav-file，请删除加载示例数据的行，并使用audioread-command取消对该行的注释。

load('speech_dft.mat');         % sample Matlab data
%[y,fs] = audioread(hfile);      % read wav-file

% Define a custom colormap
cmap = [0.4160    0.0350    0.0350;
        0.5620    0.0260    0.0260;
        0.7080    0.0180    0.0180;
        0.7810    0.0130    0.0130;
        0.9270    0.0040    0.0040;
        1.0000         0         0;
        1.0000    0.1410         0;
        1.0000    0.2120         0;
        1.0000    0.3530         0;
        1.0000    0.3880         0;
        1.0000    0.5290         0;
        1.0000    0.5650         0;
        0.9790    0.5480    0.1120;
        0.9570    0.4950    0.2240;
        0.9250    0.4170    0.3920;
        0.9040    0.3650    0.5040;
        0.8710    0.2860    0.6710;
        0.8130    0.2040    0.8160;
        0.7860    0.2010    0.7930;
        0.7060    0.1910    0.7240;
        0.5990    0.1770    0.6320;
        0.4390    0.1570    0.4940];

% Define nfft, window and noverlap
nfft     = 256;
window   = hanning(nfft);
noverlap = round(nfft/2);

% Display the spectrogram of the unfiltered signal
figure;
subplot(3,1,1);
spectrogram(y,window,noverlap,nfft,fs,'yaxis');
colormap(cmap);
title('Unfiltered signal');

% Design and apply the lowpass filter
order = 4;
fg    = 4500;
[b,a] = butter(order,fg/fs/2,'low');             % design filter
x1    = filter(b,a,y);                           % apply filter

% Display the spectrogram of the lowpass filtered signal
subplot(3,1,2);
spectrogram(x1,window,noverlap,nfft,fs,'yaxis');
colormap(cmap);
title('Lowpass filter');

% Design and apply the bandpass filter
order   = 10;
lowfreq = 2000;
hifreq  = 4000;
[b,a]   = butter(order,[lowfreq,hifreq]/(fs/2), 'bandpass'); % design filter
x2      = filter(b,a,y);                                     % apply filter

% Display the spectrogram of the bandpass filtered signal
subplot(3,1,3);
spectrogram(x2,window,noverlap,nfft,fs,'yaxis');
colormap(cmap);
title('Bandpass filter');

它产生以下结果：

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Answer 2

好的，我将给出一个更好的例子，说明注释部分中讨论的内容。我希望你觉得这很有用。基本上有一个噪声的正弦波信号。我做了一个谱图，然后过滤掉一些噪声，再做另一个谱图来显示滤波的结果。

x = 0:0.001:4*pi;
y = sin(x);
y2 = wgn(1,length(x),0.5);
y3 = sin(314*x);
y4 = y+y3+y2;

figure(1)
plot(x,y4);

nfft = 2^nextpow2(length(y4));
[S,F,T,P] = spectrogram(y4,250,50,nfft,1000);

figure(2)
spectrogram(y4,250,50,nfft,1000);

%create filter and use it on the noisy signal
[b,a] = butter(4,0.5,'low');
y5 = filtfilt(b,a,y4);

figure(3)
spectrogram(y5,250,50,nfft,1000);

以下是所生成的地块：

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正如你所看到的，谱图调用有默认的颜色缩放，你可以通过图形句柄改变颜色，如果你想知道怎么做的话，我会问另一个问题，或者谷歌它。

请听取马特在评论部分的建议，他警告说，您需要确定如何过滤wav文件。