stlspectral alia nalysis with the dftce.sharif.edu/courses/93-94/1/ce763-2/resources/root...dsp,...
TRANSCRIPT
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S t l A l i ith th DFTSpectral Analysis with the DFT
1DSP, Lecture 14
DSP, Lecture 14 2
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DSP, Lecture 14 3
DSP, Lecture 14 4
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DSP, Lecture 14 5
The Effect of WindowingThe Effect of Windowing
Consider a continuous signal of sum of two sinusoidal signals:Consider a continuous signal of sum of two sinusoidal signals:
After Sampling with on aliasing:
DSP, Lecture 14 6
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Specially, we can rewrite it as:Specially, we can rewrite it as:
Example: pf = 100 kHzθ0 =θ1=0The Length of w[n] = 64A0=1, A1= 0.75
DSP, Lecture 14 7
DSP, Lecture 14 8
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DSP, Lecture 14 9
DSP, Lecture 14 10
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DSP, Lecture 14 11
• Reduced resolution and leakage areReduced resolution and leakage are two primary effects on the spectrum
l f l i i d has a result of applying a window to the signal. g
• The resolution is influenced by the id h f i l b fW(j )width of main‐lobe of W(jω)
• The degree of leakage depends on theThe degree of leakage depends on the amplitude of side‐lobes, respect to the
li d f i l bamplitude of main‐lobe DSP, Lecture 14 12
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Design using Kaiser WindowDesign using Kaiser Window• Assume:• Δml = Width of Main‐Lobe • And Asl = the ratio of Main‐lobe to the
Largest side‐Lobe (in dB)
DSP, Lecture 14 13
The effect of spectral SamplingThe effect of spectral Sampling
DSP, Lecture 14 14
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DSP, Lecture 14 15
DSP, Lecture 14 16
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DSP, Lecture 14 17
DSP, Lecture 14 18
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The previous example, but with N=128, (Zero padding)
DSP, Lecture 14 19
The effect of windowThe effect of window
• Assuming Kaiser WindowAssuming Kaiser Window
We assume that:β= 5.48 and L=64
Then we will have:A l = 40 dB and Δ l = 0 401Asl = ‐40 dB and Δml = 0.401
Not that:
DSP, Lecture 14 20
Which is very close to Δml ( Design procedure is reverse!)
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Magnitude of DFT for N=L=64
DSP, Lecture 14 21
DFT for N=L=32
DSP, Lecture 14 22
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L= 32 But N=64
DSP, Lecture 14 23
L=32 and N=1024
DSP, Lecture 14 24
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DSP, Lecture 14 25