Who first coined "Direct Form I" and "Direct Form II"?

Question

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:

No response yet, so for now I assume it must have been "Dr. Direct" — Dan Boschen, Jun 13 '21 at 14:10
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. — robert bristow-johnson, Jun 14 '21 at 05:16
the first time i saw the terms was in m. e. van valkenburg's Network Analysis from the 1970s. — robert bristow-johnson, Jun 14 '21 at 05:19
@robertbristow-johnson thanks! This is good; please put it as an answer and it will be the correct answer until someone comes up with an earlier reference. — Dan Boschen, Jun 14 '21 at 23:16
the M.E. Van Valkenburg thing is just a memory, Dan. it is not authoratative. — robert bristow-johnson, Jun 15 '21 at 00:03
@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. — malik12, Mar 24 '22 at 14:43

malik12 · Accepted Answer · 2022-03-24T18:48:43.417

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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

edited Mar 24 '22 at 18:48

answered Mar 24 '22 at 14:42

malik12

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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") – Dan Boschen Mar 24 '22 at 18:13
@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 – malik12 Mar 24 '22 at 18:51
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I found the Golden Kaiser paper here https://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 ! – Dan Boschen Apr 12 '23 at 13:20
@DanBoschen Welcome and thank you for sharing the link! – malik12 Apr 18 '23 at 08:01

Who first coined "Direct Form I" and "Direct Form II"?

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