# filter coefficients

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Tom 2012년 5월 25일
댓글: 632541 2021년 4월 12일
Just a quick question - are 'filter coefficients' the coefficients of the impulse response, desired transfer function, or actual transfer function?
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Walter Roberson 2012년 5월 25일
This is really a filter theory question, not a MATLAB question.
Matt Fig 2012년 11월 2일
Just a quick question - are 'filter coefficients' the coefficients of the impulse response, desired transfer function, or actual transfer function?

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### 채택된 답변

Wayne King 2012년 5월 25일
That depends. The filter coefficients are the coefficients of the difference equation. If your filter is an FIR filter, then the filter coefficients are the values of the impulse response.
If you have an IIR filter, then the filter coefficients are not the same as the impulse response. Remember in that case the impulse response is infinite.
For example:
b = fir1(10,0.2);
stem(b)
h = impz(b);
stem(h)
isequal(b',h)
but
[b,a] = butter(10,0.2);
h = impz(b,a);
But the ratio of Z-transforms of the numerator coefficients to denominator coefficiens is equal to the Z-transform of the impulse response.
For example - consider the IIR system with the following difference equation
y(n)-0.8*y(n-1) = x(n)
So the filter coefficients are:
A = [1 -0.8]; B =1;
The impulse response is:
h(n) = 0.8^n*u(n) where u(n) is the unit step. But compare:
h1 = impz(B,A);
subplot(211)
stem(h1,'color',[1 0 0]);
subplot(212)
n = 0:length(h1)-1;
h = 0.8.^n;
hold on;
stem(h,'color',[0 0 1]);
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Tom 2012년 5월 25일
Thanks Wayne - I'll check all this out over the next day or two.

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### 추가 답변 (2개)

Wayne King 2012년 5월 28일
The unit step should be treated in your DSP book.
For a sequence, the unit step sequence is the sequence which is 1 for n>=0 and 0 for all n<0.
As far as your other question, I solved the difference equation. I think if you search the web, you will find plenty of material on solving difference equations. This forum does not lend itself to me walking through that solution here.
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Tom 2012년 5월 28일
hi wayne, i'm just having problems seeing how you got from the difference equation to the impulse response (the IIR example).
also i'm not familiar with the term 'unit step'.
if you could let me know how you did this step and what 'unit step' means that would be ace.
tom
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632541 2021년 4월 12일
Hi Wayne King,
How to calculate number of taps required to design bandpass filter with sampling frequency 4MHz and signal has the frequency range of 1000 Hz to 1000000Hz ..?

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