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I see "Direct Form I" and "Direct Form II" commonly in literature to refer to FIR / IIR implementation from the filter transfer function, and reference it myself, but where did that terminology first originate so that I can properly credit that person?

For example:

Direct Form II

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    $\begingroup$ No response yet, so for now I assume it must have been "Dr. Direct" $\endgroup$ Commented Jun 13, 2021 at 14:10
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    $\begingroup$ i think the "first" direct form was the "direct" realization of the current output in terms of what is known: the current and past input and the past output. with no intermediate variables. the DF2 is "canonical" (meaning the number of states is exactly what the order of the filter requires) but requires an intermediate variable which is the input to the first $z^{-1}$ state. $\endgroup$ Commented Jun 14, 2021 at 5:16
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    $\begingroup$ the first time i saw the terms was in m. e. van valkenburg's Network Analysis from the 1970s. $\endgroup$ Commented Jun 14, 2021 at 5:19
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    $\begingroup$ the M.E. Van Valkenburg thing is just a memory, Dan. it is not authoratative. $\endgroup$ Commented Jun 15, 2021 at 0:03
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    $\begingroup$ @DanBoschen I have posted the oldest reference I could find in the answer below. I see the question was posted a while back but saw it just now and got curious. $\endgroup$
    – malik12
    Commented Mar 24, 2022 at 14:43

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I think this is where the term originated:

R. M. Golden and J. F. Kaiser, "Design of wideband sampled-data filters," in The Bell System Technical Journal, vol. 43, no. 4, pp. 1533-1546, July 1964, doi: 10.1002/j.1538-7305.1964.tb04095.x.

Although there is an older reference in the paper as well, the first one mentioned in the paper, but I was unable to access and verify if that had any mention of the term "Direct Form".

Whereas the earliest usage of "Direct Form 1" and "Direct form 2" were found here:

On the Interaction of Roundoff Noise and Dynamic Range in Digital Filters* Leland B. Jackson, Feb 1970, Link here

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  • $\begingroup$ Just to confirm @Malik12, did the reference you found mention "Direct Form I" and "Direct Form II" specifically? (Or even "Direct Form 1" and "Direct Form 2") $\endgroup$ Commented Mar 24, 2022 at 18:13
  • $\begingroup$ @DanBoschen sorry I originally posted when the term "direct form" was seen, I have updated the earliest reference to "Direct Form 1" and "Direct Form 2" I saw in the answer as well but still could be wrong though as these papers are from the 60s $\endgroup$
    – malik12
    Commented Mar 24, 2022 at 18:51
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    $\begingroup$ I found the Golden Kaiser paper here archive.org/details/bstj43-4-1533/mode/2up and correct it only shows the direct form 2 structure but doesn't name it. I haven't seen the actual paper by Leland Jackson yet but know of no earlier references, so as of now my assumption is that is the first mention, thanks @malik12 ! $\endgroup$ Commented Apr 12, 2023 at 13:20
  • $\begingroup$ @DanBoschen Welcome and thank you for sharing the link! $\endgroup$
    – malik12
    Commented Apr 18, 2023 at 8:01

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