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Homework Help: Phase shift and amplitude change when put through FIR filter

  1. May 1, 2013 #1
    Hey all,
    I am having trouble with this problem:

    A sampled sinusoidal signal having a normalized frequency of 0.30π is sent through an FIR filter. The filter impulse response is,

    h[n] = 1/3δ[n] + 1/3δ[n-1] + 1/3δ[n-2]

    From this I must find out by what factor the input signal is multiplied by and what the phase shift is, (if there is in fact a phase shift).

    my current theory is:
    Let z = e^(jω) (j = i for those not in an electrical field)

    H(z) = 1/3 + 1/3*z^(n-1) + 1/3*z^(n-2)

    y[n] = H(z)*z^n

    Then I am lost from here assuming my above theory is even correct. Any help would be greatly appreciated as I have been stuck on this one for a while. :)
  2. jcsd
  3. May 2, 2013 #2

    rude man

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    Homework Helper
    Gold Member

    Do you know what "normalized frequency" means? I sure don't. It must be related to the sample time T. So assuming T = 1 then f = 0.3pi/T?
  4. May 2, 2013 #3
    Not to worry, figured it out you can obtain phase and magnitude directly from H(z), also normalised frequency is just omega divided by the sampling rate
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