How to test a low pass filter by generating a test signal?

Hi,

I have designed a simple program to read in pressure versus time data from an excel file and apply a 2 Hz low pass filter and then perform an FFT on the filtered signal. My question is this: is there a way to generate an full frequency spectrum pulse so i can test the low pass filter before moving onto my own data?

here is the code i have.

if true
% code
data = xlsread('data.xlsx');
t = data(:,1);
p = data(:,2);
subplot(3,1,1);
  plot(t,p);
  title('Original waveform')
  xlabel('Time (seconds)')
  ylabel('Pressure (mmHg)')
fs=1000 %sample Freuency 
fn=fs/2; % Nyquist Frequency 
fc=2; % Desired Cutoff frequency (example)
[b,a]=butter(2,fc/fn); % IIR Filter coefficients, b=num, a=denom 
xf=filter(b,a,data); % apply filter to x
subplot(3,1,2);
  plot(t,p);
  title('2 Hz low pass')
  xlabel('Time (seconds)')
  ylabel('Pressure (mmHg)')
L = length(xf);
NFFT = 2^nextpow2(L); % Next power of 2 from length of y
Y = fft(xf,NFFT)/L;
f = fs/2*linspace(0,1,NFFT/2+1);
% Plot single-sided amplitude spectrum.
subplot(3,1,3);
  plot(f,2*abs(Y(1:NFFT/2+1))) 
  title('Single-Sided Amplitude Spectrum of y(t)')
  xlabel('Frequency (Hz)')
  ylabel('|Y(f)|')
  % code
end

Answer 1

[Star Strider]

Use the freqz function:

[h,w] = freqz(b,a,100);
figure(1)
subplot(2,1,1)
plot(abs(h))
subplot(2,1,2)
plot(w)

[Eoghan]

thanks for the answer.

[Star Strider]

My pleasure!