Monday, June 19, 2017


  • First bug report, by Erick Gallun: in first sentence of section 6.2, "to an output function to time" should be "to an output function of time." He gets the first bug bounty dollar, and my thanks (note that I edited this post after he commented below; hope that's not confusing).
  • Jeff Rector earns a dollar for spotting "simultaeous", which should be "simultaneous", in section 4.5, page 55. 
  • Tomek Maka earns a buck for the misformatted equation (paren in wrong place) in the box "Example: Delay Lines and Moving-Average Filters" in chapter 12, page 220.  Should be H(s)=\frac{Y(s)}{X(s)}=\exp(-sT). 
  • Tomek Maka finds one more stray paren:  "h(t))" has an extra close paren, middle equation on page 123.
  • Responding to my challenge to readers on section 17.2, André van Schaik reported the typo on page 311, second paragraph, where "a sampling term" should be "a damping term".
  • Two bugs from Wan-Teh's comment below: 
    • P.128, Sec. 7.5: In the second-to-last equation on this page: H(z)X(z) = Z{h(k) * x(k)} should have square brackets for indices, as H(z)X(z) = Z{h[k] * x[k]}.  
    • P. 132, Sec. 7.7: In the box "Detail: Zeros at the Origin", the last paragraph says: "s-domain points that would map to z = 0 are infinitely far to the right side in the s plane" – "right" should be changed to "left".
  • Roy Patterson reports a flubbed wording in the last paragraph of Chapter 20, p. 354: "continue to get away with ignore" should be "continue to ignore", or possibly "continue to get away with ignoring".  I'll add a dollar to the envelope I'm taking to give him in Cambridge.
  • A few errors and nits that I've found myself, that I'll fix in a later printing if I can.
    • Section 2.2 p. 26 "introduced below as" should really refer to a section: "introduced in section 2.5 as".
    • Section 2.3 p. 27 "as "Cooper et al. (2008) summarizes", should use the plural verb "summarize" (because in my style, I interpret the subject here as the authors, plural, not the paper, singular).
    • Figure 3.4. The dotted lines connecting the parts of the figure are too light to see.
    • Before the lower box on p. 224, "we studies" should be "we studied".
    • In the Physics Connection box on p. 228, "nonmoving sinusoidal spatial envelopes" should be singular.
    • In the box "On Quasi-Linear Filters" on p.240, "auditory filters models" should be "auditory filter models".
    • Figure 16.6 caption refers to "the middle damping" where it should say "the lowest damping"; or I could change the figure to match the caption.
    • Section 18.3, p. 328, "input to the ICS." should be "input to the IHCs."
    • In the box "History Connection: From IPD to ITD", p. 382, Figure 22.1 and caption have been placed badly, between the sentence introducing a quote and the quote.
    • Figure 25.1 caption, p. 443, "possbiility" should be "possibility".
I expect we'll find more.  Respond here or email me.

Here are bugs found in 2018, after the corrected PDF was out:

  • Binary logarithmss has an extra "s"; Chapter 3, box The Mathematics of Logarithms and Power Laws, second paragraph (p.34 in hardback); reported by Ben Caswell-Midwinter
  • Hershel is a misspelling of Herschel, and the Herschel 1930 ref should be 1830, in section 4.8 (p.67 in hardback).


  1. I'm not to section 17 yet, but this sentence from 6.2 should be fixed.
    "A system is a device or a mathematical abstraction that maps an input function of time to an output function to time."

  2. Hi Dick,

    Really nice job on the book! The erroneous word in 17.2 is ‘sampling’ in the first line of the second paragraph on p 311. Should be ‘damping’.


  3. Thanks, André, you get that dollar!

  4. Hi Dick,

    I'd like to report two errors in Chapter 7.

    1. P.128, Sec. 7.5: In the second-to-last equation on this page:

    H(z)X(z) = Z{h(k) * x(k)}

    Square brackets, not parentheses, should be used with the discrete-time signals h and x:

    H(z)X(z) = Z{h[k] * x[k]}

    2. P. 132, Sec. 7.7: In the box "Detail: Zeros at the Origin", the last paragraph says:

    ...; s-domain points that would map to z = 0 are infinitely far to the right side in the s plane, ...

    "right" should be changed to "left".

    I found a webpage that describes the s plane to z plane mapping in detail:

    Wan-Teh Chang

  5. Thanks, Wan-Teh, for these and all your many previous pre-publication bug reports. More dollars coming your way.

  6. Hi Dick,

    thanks for the excellent book! I just want to comment on the
    impulse-invariant Gammatone design, which I think is not described correctly. Applying the Z transform on the sampled Gammatone filter impulse response yields both poles and zeros, not only poles. The difference between the all-pole design and the impulse-invariant design with poles and zeros, however, is rather small, at least for filters with center frequencies not too close to the Nyquist frequency.

    Volker Hohmann

    1. I've been talking this over with Volker and encouraging him to post here; but when he tried it didn't work, so I had to open up anonymous comments, and now it does. He's right, and fixing this is complicated. I'm working on a short paper on the impulse invariance method, to acknowledge my error, fix it, and see how much it matters (not a lot, fortunately).