DSP - Frequency Response of an FIR Filter

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Discussion Overview

The discussion revolves around the frequency response of a linear time-invariant (LTI) filter defined by a specific difference equation. Participants are exploring how to derive the frequency response, plot its magnitude and phase, and address challenges related to complex numbers in the context of digital signal processing (DSP).

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents the difference equation and attempts to derive the frequency response, expressing it as H(e^-jw) = 1 - e^-j2w.
  • The same participant expresses uncertainty about how to plot the magnitude of the frequency response, particularly regarding the presence of the imaginary unit j in the expression.
  • Another participant suggests a resource on complex numbers that may assist with understanding the polar form.
  • A different participant questions the interpretation of the magnitude, suggesting that cos(w) is always zero based on their understanding of the expression 2jsin(w).
  • One participant shares a reference document that discusses plotting complex functions and suggests separating the plots for magnitude and phase for clarity.

Areas of Agreement / Disagreement

The discussion includes multiple viewpoints regarding the interpretation of the magnitude and phase of the frequency response. There is no consensus on how to handle the imaginary component in the magnitude or how to effectively plot the results.

Contextual Notes

Participants have not fully resolved the mathematical steps involved in plotting the frequency response, particularly concerning the treatment of complex numbers and the implications for the magnitude plot.

Who May Find This Useful

This discussion may be useful for students and practitioners in digital signal processing, particularly those interested in understanding frequency response analysis and complex function plotting.

Lightning19
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Homework Statement


A linear time-invariant filter is described by the difference equation

y[n] = x[n] - x[n-2]

a) Obtain an expresson for the frequency response of this system.

b) Sketch the frequency response (magnitude and angle) as a function of frequency.


2. The attempt at a solution

a) {bk} = {1, 0, -1}
H(e^-jw)= 1-e^-j2w

b) I am not sure how to plot the magnitude.

H(e^-jw)= 1-e^-j2w = (e^-jw)(2*j*sin(w))

where (e^-jw) is the angle and (2*j*sin(w)) is the magnitude.

However, there is an imaginary number, j, in the magnitude...what do I do with this?

Thank you.
 
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OK... so from the notation is seems like cos w is always 0 since the magnitude is

2jsin(w)

So would it just be an empty set of axis?
 
I did a little googling to see if I could find a good reference for plotting complex functions in regards to frequency response. Here's a pdf on FEEDBACK CONTROL that's a bit long but has a good explanation on page 147.
We can replot the data by separating the plots for magnitude and
phase making two plots versus frequency...
"www.ece.clemson.edu/crb/ece409/PlettNotes/PlettDawson.pdf"[/URL]

Regards
 
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