[英]Plotting Frequency Spectrum using Matlab with hold function
Suppose I have successfully generated a Single-sided Power spectrum as follows: 假设我已经成功生成了单边功率谱,如下所示:
X_mags = abs(fft(signal));
bin_vals = [0 : N-1];
fax_Hz = bin_vals*fs/N;
N_2 = ceil(N/2);
plot(fax_Hz(1:N_2), 20*log10(X_mags(1:N_2)));`
now I want to plot a second graph on top of the first one: 现在我想在第一个图形上绘制第二个图形:
hold on;
Lastly I perform an LPC analysis on the signal and calculate the frequency response. 最后,我对信号进行LPC分析并计算频率响应。 The frequency response should be plotted on top of the Power spectrum, so:
频率响应应绘制在功率谱的顶部,因此:
[a, g] = lpc(signal,N);
[h,f] = freqz(b,a,N,fs);
plot(?);
For the sake of simplicity, let's assume the parameters are all correctly given, how should I write the plot function for having a correct display of the frequency response? 为了简单起见,假设所有参数均正确给出,如何编写绘图函数以正确显示频率响应? A simple plot(f) doesn't work.
简单的绘图(f)不起作用。
Can someone explain why? 有人可以解释为什么吗? Thanks
谢谢
The response h
is complex, so you'll want to get the magnitude of the response via multiplication by its complex conjugate.: 响应
h
很复杂,因此您需要通过乘以其复共轭来获得响应的大小。
plot(f, 10*log10(h.*conj(h)));
Note the use of 10*log10 because the operation above squares the amplitude response held in h
. 请注意使用10 * log10,因为上面的运算将保持在
h
的幅度响应平方。
Or, if you're less interested in being pedantic about working with complex numbers, you could just take the absolute value of the complex values, being sure to 20*log10 because the abs
does not square the values 或者,如果您对处理复数不太感兴趣,则可以取复数值的绝对值,并确保为20 * log10,因为
abs
不会使数值平方
plot(f, 20*log10(abs(h)));
A simple plot(f)
tries to plot frequency vector, isn' t it? 一个简单的
plot(f)
试图绘制频率矢量,不是吗?
Check the code below: 检查以下代码:
X_mags = abs(fft(signal));
bin_vals = [0 : N-1];
fax_Hz = bin_vals*fs/N;
N_2 = ceil(N/2);
[a, g] = lpc(signal,N);
[h, f] = freqz(b, a, N, fs);
figure,
hold on,
plot(f, 20*log10(abs(h)), 'r');
plot(fax_Hz(1:N_2), 20*log10(X_mags(1:N_2)));
title('Frequency Spectrum');
xlabel('Frequency (Hz)');
ylabel('Amplitude (dB)');
legend('Frequency Response', 'Single-sided Power spectrum')
Btw, there is a MATLAB function db()
for decibel calculation. 顺便说一句,有一个用于分贝计算的MATLAB函数
db()
。 That might be useful. 那可能有用。
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