Filtering & Aliasing - week 5
- Created by: harveyf2801
- Created on: 13-01-21 22:51
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- Filtering and Aliasing
- Filters
- The ideal anti-aliasing filter is a brick wall low-pass at the Nyquist frequency
- Filter should be applied before sampling
- Characteristics
- The region of minimal attenuation is called a pass-band (unity)
- Half-power point is at -3dB
- The steepness of a filter is called the roll-off rate
- 20 x n dB per decade
- 6 x n dB per octave
- The region of unwanted signal is called a stop-band
- The order determines the roll off
- Order = roll-off (octave) / 6
- Order = roll-off (decade) / 20
- Transfer functions
- Butterworth
- Bessel
- Chebyshev
- Ripple (gain) in stop- or pass-band
- Types
- Band pass (BP) attenuates frequencies in the stop-band above and below certain cut offs
- Low pass (LP) attenuates frequencies above the cut off
- High pass (HP) attenuates frequencies below cut off
- Band stop (BS) attenuates frequencies in the stop-band between certain cut offs
- Aliasing
- Also called frequency fold-back
- Oversampling can be used to reduce aliasing
- Key considerations
- Amount of attenuation in pass-band
- No phase distortion in pass-band
- Desired filter roll-off in stop-band
- Steepness in transition region
- Note how this affects different frequencies and the ripple
- Filters
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