Low-pass differentiating FIR filter design¶
What it does¶
This utility designs a linear-phase FIR filter that differentiates low-frequency signal content while attenuating higher frequencies.
When to use it¶
Use it when a processing chain requires a reproducible low-pass differentiator with an explicit constant delay.
Canonical ID: tools.lpd_filter
Inputs¶
| Name | Meaning | Type | Unit | Requirements |
|---|---|---|---|---|
sampling_frequency |
Sampling frequency for which the differentiating filter is designed. | real scalar | Hz | greater than: 0; no NaN; finite |
stop_frequency |
Frequency at which the low-pass differentiating response reaches its stop band. | real scalar | Hz | greater than: 0; no NaN; finite |
Parameters¶
| Name | Meaning | Type | Unit | Default | Requirements |
|---|---|---|---|---|---|
pass_frequency |
Optional end of the differentiating pass band. | real scalar | Hz | stop_frequency - 0.2 |
greater than: 0 |
order |
Even FIR filter order. | integer scalar | sample | automatic |
greater than: 0 |
Outputs¶
| Name | Meaning | Type | Unit |
|---|---|---|---|
filter_coefficients |
FIR numerator coefficients of the designed differentiating filter. | real vector | 1/s |
delay |
Constant linear-phase delay introduced by the FIR filter. | real scalar | sample |
How it works¶
The requested sampling, pass, and stop frequencies define an even-order antisymmetric FIR response. The returned delay can be used to align the filtered signal with the original samples.
Interpretation and limitations¶
The coefficients are tied to the requested sampling frequency and should be redesigned when it changes. The delay must be handled explicitly in causal processing chains.
References¶
- Jesús Lázaro et al. (2014). Pulse rate variability analysis for discrimination of sleep-apnea-related decreases in the amplitude fluctuations of pulse photoplethysmographic signal in children. IEEE Journal of Biomedical and Health Informatics. doi:10.1109/JBHI.2013.2267096