Intro to the issue

We are currently having two temporal filter related fields in the electrophysiology specification:

• SoftwareFilters
• HardwareFilters

both fields have a description as follows (with slight adjustments), please focus on the specification of filters:

list of temporal software filters applied. Ideally key:value pairs of pre-applied software filters and their parameter values: e.g., {"Anti-aliasing filter": {"half-amplitude cutoff (Hz)": 500, "Roll-off": "6dB/Octave"}}. Write n/a if no software filters applied.

So we can always use a string "n/a".

Beyond that, the information is a bit confusing, as identified by @effigies in https://github.com/bids-standard/bids-specification/pull/322/files#r321275320.

We are asking for a list, which brings to mind an array of the following form:

{
    "myKey": ["val1", "val2", 45455.3, {"obj": 1}]
}

However, in the validator and our examples (e.g., starter kit), we are requiring an "object of objects" in the form:

{
    "HardwareFilters": {"HighpassFilter": {"CutoffFrequency": 0.1}}
}

questions

Should we:

1. stay with our current way to specify filters and simply clarify the language in the specification to drop the word "list", and use "object of objects" or similar?
2. change the way we specify filters to be a "list of objects" --> this would allow the benefit to intuitively specify the order of how filters were applied to the data
3. allow both and change validator and spec text accordingly

I am not a signal processing expert ... but as long as the order in which filters are applied is irrelevant (e.g., because they are linear operations), I am in favor of option 1.