Questions on filter coefficient and fir

% FIR Low pass filters using rectangular, triangular and kaiser windows % sampling rate - 8000 order = 30; cf=[500/4000,1000/4000,1500/4000]; cf--> contains set of cut-off frequencies[Wc ] % cutoff frequency - 500 b_rect1=fir1(order,cf(1),boxcar(31)); Rectangular b_tri1=fir1(order,cf(1),bartlett(31)); Triangular b_kai1=fir1(order,cf(1),kaiser(31,8)); Kaisar [Where 8-->Beta Co-efficient] % cutoff frequency - 1000 b_rect2=fir1(order,cf(2),boxcar(31)); b_tri2=fir1(order,cf(2),bartlett(31)); b_kai2=fir1(order,cf(2),kaiser(31,8)); % cutoff frequency - 1500 b_rect3=fir1(order,cf(3),boxcar(31)); b_tri3=fir1(order,cf(3),bartlett(31)); b_kai3=fir1(order,cf(3),kaiser(31,8)); fid=fopen('FIR_lowpass_rectangular.txt','wt'); fprintf(fid,'\t\t\t\t\t\t%s\n','Cutoff -400Hz'); fprintf(fid,'\nfloat b_rect1[31]={'); fprintf(fid,'%f,%f,%f,%f,%f,%f,%f,%f,%f,%f,\n',b_rect1); fseek(fid,-1,0); fprintf(fid,'};');

Q.1 In the above code the line cf=[500/4000,1000/4000,1500/4000]; Why this has been added? Q.2 what is the formula of Cutoff frequency? Q.3 How the matlab generates the coefficients internally? Q.4.what is the difference between rectangular and Kaisar window other than Beta?

[Jan]

Please format your code using the "{} Code" button. Then it will be readable.

Answer 1

[Jan]

Q1. As the comment tells you "cf contains [a] set of cut-off frequencies[Wc]" It has been added, because the programmer needed a set of cut-off frequencies.

Q2. The formula of cut-off frequency depends on the filter parameters.

Q3. Which coefficients? You can look inside the code of the functions. Explaining all of the hundreds of code lines here in the forum would be a bad idea.

Q4. I'm not sure, how to answer this. I'd take a look at https://en.wikipedia.org/wiki/Window_function

Sorry, edgate16 texas instrument, I do not really understand your questions.

[edgate16 texas instrument]

Q.1.In the code itself why they have divided by 4000 while calculating cf?If the cut-off frequency is 500 or 1000 or 1500 why they have divided by 4000? Q.2.Can I chose any cut-off frequency for a filter? Q.3.I want to know that matlab is generating coefficients but on which factors it is generating i.e is there any formula for generating those coefficients?

Sir,please answer me as soon as possible.

[Jan]

"As soon as possible" is inpolite. Do not try to push voluntary helpers.

Q1. The frequencies are normalized by the half sampling rate, which is 8000. Therefore the values are divided by 4000.

Q2. It depends on what exactly "a filter" means: The filter method including the window type and its parameters determine the cut-off frequency.

Q3. Of course there are formulas to calculate the coefficients. You can find the calculations in the code of the functions. Look e.g. in edit kaiser, edit fir1 etc.

[edgate16 texas instrument]

Sorry sir mentioning that sentence.Thank you for answering my questions. Sir, I have a question Q.1.Coefficients are nothing but the impulse response given to the filter.Suppose the coefficient=0.00234 does it represent at coefficient value =0.00234 the amplitude of the impulse signal is 1 or something else?

If you are free kindly answer me sir.