2nd Order Band-Pass Filter
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| Figure 1 (a): FilterBandPass2 amplitude versus log(frequency) with 440 Hz peak frequency and 6 Hz. bandwidth. | Figure 1 (b): FilterBandPass2 log(amplitude) versus log(frequency) with 440 Hz peak frequency and 6 Hz. bandwidth. |
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| Figure 2 (a): FilterBandPass2 amplitude versus log(frequency) with 440 Hz peak frequency and 25 Hz. bandwidth. | Figure 2 (b): FilterBandPass2 log(amplitude) versus log(frequency) with 440 Hz peak frequency and 25 Hz. bandwidth. |
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| Figure 3 (a): FilterBandPass2 amplitude versus log(frequency) with 440 Hz peak frequency and 100 Hz. bandwidth. | Figure 3 (b): FilterBandPass2 log(amplitude) versus log(frequency) with 440 Hz peak frequency and 100 Hz. bandwidth. |
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| Figure 4 (a): FilterBandPass2 amplitude versus log(frequency) with 440 Hz peak frequency and 400 Hz. bandwidth. | Figure 4 (b): FilterBandPass2 log(amplitude) versus log(frequency) with 440 Hz peak frequency and 400 Hz. bandwidth. |
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| Figure 5 (a): FilterBandPass2 amplitude versus log(frequency) with 440 Hz peak frequency and 1600 Hz. bandwidth. | Figure 5 (b): FilterBandPass2 log(amplitude) versus log(frequency) with 440 Hz peak frequency and 1600 Hz. bandwidth. |
Figures 1 (a) through 5 (b) plot frequency responses for the FilterBandPass2 unit. The (b) graphs are plotted to a common vertical scale, but the scale in each (a) graph is sized so that the respose curve peaks near the top of the vertical axis.
Notice that these graphs all contain substantial leftward tails. This feature stands in contrast to the 2nd Order Butterworth Band-Pass Filter. It means that frequencies below the peak band are never fully suppressed — not an ideal characteristic for the “band-pass” role. It also means that the FilterBandPass2 unit makes a terrible high-pass filter.
The up side of the leftward tail is that when used in cascade, this filter produces a multi-peak frequency-response profile with more-pronounced . This effect is explored graphically on the page devoted to Cascaded Digital Filters.
| © Charles Ames | Page created: 2014-02-20 | Last updated: 2015-07-12 |