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Basic information about FIR filter

Please tell me:
1. what is "impule responce"?
2. what is tap (4 tap filter)?
3. what do coefficients do in FIR?
4. what is a "delay" ?
 
T

Tim Wescott

Jan 1, 1970
0
Please tell me:
1. what is "impule responce"?

"impulse", not "impule". In the sampled-time domain an impulse is 1 at
sample number 0 and zero everywhere else. An impulse response is what
the filter output does in response to an impulse on the input.
2. what is tap (4 tap filter)?

The usual way we think about FIR filters is that there's an embedded
delay line, so at sample time n we have access to sample n-1, n-2, n-3,
and so on, for as many prior samples as we need. Strictly speaking a
'tap' is any point in the delay line where the filter uses the data, but
what people usually mean by 'taps' is the number of delays plus one -- so
a four tap filter would use sample n, sample n-1, sample n-2 and sample
n-3.
3. what do coefficients do in FIR?

They determine the behavior of the filter. If x_n is the signal at
sample n and a_m is the m'th coefficient, then your four-tap FIR filter
can be expressed as

y_n = a_0 * x_n + a_1 * x_{n-1} + a_2 * x_{n-2} + a_3 * x_{n-3}
4. what is a "delay" ?

See my answer to 2.

One further note: if you're going to do much DSP, you may want to start
paying attention to comp.dsp -- this group has good DSP people, but
there's more on comp.dsp, and fewer flame wars to distract you.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
 
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