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I'm reading through the 3rd edition of John G. Proakis Digital Signal Processing and I came across a possible errata in Figure 2.35c on page 116. I couldn't find any errata sheet on the publisher's or author's website. It appears to me that the "-a1" and "-a2" labels on the diagram on Figure 2.35c are swapped when compared to the difference equation shown for Equation 2.5.16. I don't have access to the latest 5th edition of the book but the labeling is unchanged in the 4th edition. I just want to make sure I'm not missing some nuance of the transformation from the "Direct form I structure" to the "Direct form II structure" version of the diagram. Thanks.

Proakis Digital Signal Processing Third Edition Figure 2.35c

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  • $\begingroup$ Unless I’m also missing a subtlety, I’d say they’re swapped, yes. $\endgroup$
    – Jdip
    Jul 15, 2023 at 9:42

1 Answer 1

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You're right, there's not doubt that the indices of the coefficients in the figure don't match the given difference equation. The input-output equation of the system shown in the figure is

$$y[n]=b_0x[n]-a_2y[n-1]-a_1y[n-2]$$

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