Matlab mixed IIR Filter

I need help to design the next IIR filter:

The input signal is composed of 1Hz and 30Hz sine waves. The signal sampling frequency is 100Hz and a total of 480 points are sampled. Signals below 7Hz are removed by the IIR.

There are 480 samples. Sample 0~159 are 30Hz sine waves, sample 160~319 are 1Hz sine waves and sample 320~479 are 30Hz sine waves.

I tried to do, but it looks not correct.

fs=100                 % sampling frequency
f1=1        
f2=30 % frequency of the signal
t=20                     % time duration
n=[0:1/fs:t]            % sample period
x1=sin(2*pi*f1*n)       % single tone signal
subplot(3,1,1)
plot(n,x1)
x2=0.5*sin(2*pi*f2*n)
grid on
title('Sinusoidal signal');
% lssnew = merge(lss1,...,lssN) 
z =  [x1;x2];        % merge 2 signals
subplot(3,1,2)
plot(n,z)

Could someone give me an example how I can do it?

Thank you in advance.

[Askic V]

This is very unusual description of a problem. I assume you have samples in an array, so if you know for sure which samples are from sine waves 7 Hz or below (in this case 1 Hz), you just remove them from the array

samples_arr(161:320) = []

In Matlab, indexing starts with 1 and not 0 like in most other programing languages.

But if you need to design IIR filter, then I suggest you to check the following thread:

https://www.mathworks.com/matlabcentral/answers/284804-how-to-design-iir-highpass-filter-with-cutoff-frequency-of-20hz-and-fir-bandpass-filter-with-cutoff

[AndyK]

Thank you for your support. This is an example from the Holtek manual, which describes Cortex DSP programming. I want to design this IIR filter and then to compare Cortex DSP with Matlab filter. I have never worked with Matlab before and I'm going thru examples. Do you know how to combine these two signals (I need a function)

Answer 1

[Mathieu NOE]

hello

try this

this can be genralizd for a arbritary sequence of x1 / x2 signals

NB that a sampling frequency of 100 Hz is a bit low to reproduce a 30 Hz tone with a good accuracy ; would rather suggest to increase to 300 Hz at least

fs=100;                 % sampling frequency
f1=1;        
f2=30; % frequency of the signal
% t=20                     % time duration

samples = 160 ; % for each block of data for 1 frequency
dt = 1/fs;
t = (0:samples-1)*dt;            % sample period
x1=sin(2*pi*f1*t);       % single tone signal
x2=0.5*sin(2*pi*f2*t);


figure
subplot(3,1,1)
title('Sinusoidal signal');
plot(t,x1)
subplot(3,1,2)
plot(t,x2)
grid on
z =  [x1 x2 x1];        % merge 3 signals
tz = (0:3*samples-1)*dt; % time for 3 signals
subplot(3,1,3)
plot(tz,z)