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Filters

This directory contains FIR filter designs.

Files ending in a .fda extension are the design files associated with the MATLAB Filter Design & Analysis Tool.

The .mat files are the exported filter taps. These are intended to be loaded in MATLAB or Octave to view and analyze filter responses.

The .json files are the resulting filter specifications used by OOKiedokie.

In general, these files are named based upon their pass-band, stop-band, and decimation characteristics. Because different hardware will utilize different sample rates, these are expressed in terms of the sample rate, Fs.

The preferred naming scheme is:

<pass_band>_<stop_band>[_decimation].json

For example, for a filter file with a passband at Fs/32 and a stop band at Fs/4, with no decimation (i.e., decimation by 1):

Fs32_Fs4.json

And for the same filter with decimation by 2:

Fs32_Fs4_dec2.json

Filter file format

The FIR filters designed used by OOKiedokie are specified via JSON files. Below is a filter design specification consisting of a single unity stage:

{ "filter": {
    "comment": "This filter is an example.",

    "stages": [
        {
            "decimation": 1
            "taps": [ 1.0 ]
        }
    ]
}}

The filter must begin with a top-level object named filter. This is enforced by OOKiedokie and is used as a simple means to provide feedback if the wrong .json file is provided.

The comment string is optional, but recommended. Use this to briefly describe the design and its association with any design files (e.g., MATLAB fdatool files).

Next, the filter specification contains a stages array. This is required, even if the filter only contains a single stage.

Each item in the stages array describes a filter stage object consisting of a decimation factor and feed-forward taps array. The decimation entry is optional, and defaults to 1 if not specified. This value must be an integer greater than or equal to 1. The taps array is required, and should included FIR filter taps specified as floating point values.

For a slightly larger example, see fs128_fs16_dec4.json.