2nd Order Band-Reject Filter
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| Figure 1 (a): FilterBandReject2 amplitude versus log(frequency) with 440 Hz notch frequency and 6 Hz. bandwidth. | Figure 1 (b): FilterBandReject2 log(amplitude) versus log(frequency) with 440 Hz notch frequency and 6 Hz. bandwidth. |
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| Figure 2 (a): FilterBandReject2 amplitude versus log(frequency) with 440 Hz notch frequency and 25 Hz. bandwidth. | Figure 2 (b): FilterBandReject2 log(amplitude) versus log(frequency) with 440 Hz notch frequency and 25 Hz. bandwidth. |
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| Figure 3 (a): FilterBandReject2 amplitude versus log(frequency) with 440 Hz notch frequency and 100 Hz. bandwidth. | Figure 3 (b): FilterBandReject2 log(amplitude) versus log(frequency) with 440 Hz notch frequency and 100 Hz. bandwidth. |
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| Figure 4 (a): FilterBandReject2 amplitude versus log(frequency) with 440 Hz notch frequency and 400 Hz. bandwidth. | Figure 4 (b): FilterBandReject2 log(amplitude) versus log(frequency) with 440 Hz notch frequency and 400 Hz. bandwidth. |
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| Figure 5 (a): FilterBandReject2 amplitude versus log(frequency) with 440 Hz notch frequency and 1600 Hz. bandwidth. | Figure 5 (b): FilterBandReject2 log(amplitude) versus log(frequency) with 440 Hz notch frequency and 1600 Hz. bandwidth. |
Figures 1 (a) through 5 (b) plot frequency responses for the FilterBandReject2 unit with a notch frequency of 440 Hz. The (a) graphs are plotted to a common vertical scale. A second vertical scale is common to the (b) graphs.
Figures 3 (a-b), with a bandwidth of 100 Hz., displays an effective notch. Wider than that bandwidth, and the notch disappears.
The low-frequency range to the left of the notch has a flat response, which is good. The frequency response to the right of the notch increases at a rate of 6.4 dB/octave, which is not good.
The continual gain rightward of the notch frequency suggests that this filter will be very tricky to use. Ways of mitigating this effect by combining FilterBandReject2 unit with other digital filters are explored on the page devoted to Cascaded Digital Filters.
| © Charles Ames | Page created: 2014-02-20 | Last updated: 2015-07-12 |