This data file contains data necessary for defining the filter’s frequency response curve (frequency vs. filter attenuation). The following table describes each of the filter data file keywords, their valid values, and default value if applicable.
External Filter Data File Keywords
| Keyword | Description | Valid Values | Default Value |
|---|---|---|---|
| ExternalFilter v1 | Indicates the data format and version of the data format. This must be the first line in the file. | ||
|
FilterDataInterpOrder |
Interpolation order for computing the filter attenuation at frequency points that fall between points specified in the data file. Order 1 is the most stable. Higher order curve fitting can cause oscillation (ringing) in the computed data, especially when the original data points have sudden changes in values. |
1 – 5 |
1 |
|
FilterDataScale |
Indicates whether the filter attenuation values are given as dB or linear values. |
dB or Linear |
dB |
|
NumFilterDataSamples |
The number of sample values, followed by two columns of data representing frequency values (column 1) and the filter attenuation response values (column 2). There must be NumFilterDataSamples number of rows in the table. The samples must be in Hz. |
> 1 |
N/A |
The data samples must follow the keyword NumFilterDataSamples and must consist of frequency/filter attenuation pairs separated by white space. The frequency values must be in Hertz units, and must be increasing in value. If the keyword FilterDataScale is set to linear, the attenuation values must be in the range 0 to 1.
Sample External Filter Data File Format
ExternalFilter v1 FilterDataInterpOrder 1 FilterDataScale Linear NumFilterDataSamples 19 -10.0e6 0.0 -9.0e6 1.0 -8.0e6 0.0 -7.0e6 1.0 -6.0e6 0.0 -5.0e6 1.0 -4.0e6 0.0 -3.0e6 1.0 -2.0e6 0.0 0.0 1.0 2.0e6 0.0 3.0e6 1.0 4.0e6 0.0 5.0e6 1.0 6.0e6 0.0 7.0e6 1.0 8.0e6 0.0 9.0e6 1.0 10.0e6 0.0
The above external filter data file will produce the following filter frequency response graph:
