# Why I Wrote My “Understanding Digital Signal Processing” Book

Why I Wrote My “Understanding Digital Signal Processing” Book

by Richard Lyons

Some time ago Charan asked me what events led me to write my “Understanding Digital Signal Processing” book? For Charan, and in case anyone else is interested, here’s the story.

In the mid-1980s I wanted to learn digital signal processing (DSP). As I tried to learn DSP it was the best of times, it was the worst of times. It was a period of understanding, it was a period of confusion, it was the season of Light, it was the season of Darkness, it was the spring of hope, it was the winter of despair, I had everything before me, I had nothing before me, I was approaching enlightenment, I was doomed to ignorance. There were kings of DSP with large jaws and mathematical minds on their thrones in universities bestowing their knowledge in cryptic form. In their ivory castles, it was clearer than crystal to the lords of technology that things were settled forever.

With thanks and apologies, to Charles Dickens, I’ll stop “clowning around” and just say that decades ago was a dismal time to try to learn DSP on one’s own. The available DSP textbooks in the mid-1980s were, for practical purposes, unreadable.

Back then, written explanations of DSP theory appeared in one of two forms: (1) mathematical miracles occur where you’re simply given a short-n-sweet equation without further explanation; or (2) you faced a flood of complex variable equations and phrases such as “it is obvious that”, “such that W(f)? Åf”, and “with judicious application of the homogeneity property.” In their defense, those DSP authors provide the needed information, but too often the reader had to grab a pick and shovel, put on a miner’s helmet, and try to dig the information out of a mountain of mathematical expressions.

How many times have you been forced to follow the derivation of an equation, after which the author states they’re going to illustrate that equation with a physical example, which turns out to be just another equation? Anyway, in the mid-1980s I needed help, other than cryptic textbooks, to learn DSP.

If you’re still with me, here’s why I wrote my DSP book. In 1987 I took an evening community college course on the subject of DSP. The class textbook wasn’t too awful bad. After reading its material 2-3 times, some of its DSP theory began to slowly sink into my head. The second half of the textbook was a series of applications notes from various hardware vendors. (I suppose the co-authors needed some “filler” material to make the page count of their book acceptable to any publishing companies we were thinking of getting in touch with). In any case, I happened to find a significant conceptual error in one of those application notes with regard to the topic of periodic sampling. You see, at that time I had spent months on my own studying periodic sampling. It was the only DSP topic that I understood at the time. (In 1988 I wrote a ‘periodic sampling’ article for the “Test and Measurement” magazine.)

Finding that major error in the textbook was a pivotal moment for me. It made me realize that textbook authors aren’t Gods after all! Maybe they’re smarter than me, and maybe they aren’t. If they’re so smart, why didn’t they catch that important periodic sampling error?

Well, …in 1990 I had a wild idea and wrote a letter to the primary author of my evening DSP class textbook, a professor at a university on the east coast of the United States. I volunteered to write a chapter on periodic sampling for the next edition of his book, assuming there might be a new edition.

In my letter to the professor I explained my idea. He requested my periodic sampling material and assured me that he’d review it and not plagiarize any of it. Cautiously excited, I thought, “Hey Rick, if you work hard enough you might actually get your name listed as a co-author of a book.”

After refining, and expanding, my periodic sampling material I mailed it to the professor. I waited and waited for a reply. Well, I *NEVER* heard from the good professor again! He returned none of my phone calls nor answered any of my subsequent letters. (There was no such thing as e-mail at that time.) In early 1991 I decided, “Heck with the professor, I’ll write my own book.” So I did.

To answer the question in the title of this blog, I wrote my first DSP book out of an untested, and unsupported, optimism that I could explain the basic concepts of DSP better than the DSP books available in 1991. I finished writing the book’s first edition and submitted that manuscript to my publisher in 1996. (In case you’re doing the math, yes, it took me five years to produce that first edition.)

Two years later, in late 1998, I found the east-coast professor’s E-mail address on the Internet. Being my cantankerous self, I sent him the following E-mail thanking him for ignoring me all those years ago. (Out of common decency I won’t give the professor’s name here. If you want to know his name, contact the NSA. I’ll bet they have a copy of my e-mail.) Here’s the content of my e-mail:

From: rick lyons To: Professor@xxx.edu

Date: 12/10/98 08:16:19

Dear Professor,

I owe you a debt of gratitude. In May of 1990 I wrote you a letter

in which I volunteered to contribute some material to the (at that

time) next edition of your digital signal processing textbook. You

answered my letter and encouraged me to forward my material (on

periodic sampling) for your review, and you assured me that you’d

not plagiarize any of that material. I did mail my periodic sampling

text and figures to you in late May, 1990. After that, you failed

to return any of my phone calls, or respond to any of my subsequent

letters. This disappointed and annoyed me so much that I became

stubborn and decided to write my own DSP book.

My book (“Understanding Digital Signal Processing”) was published a

few years ago and has been surprisingly successful. So successful, in

fact, that it’s changed my life for the better. Had you answered

my phone calls or letters, I’d still be working 45 hours per

week for some aerospace company. Now I spend my time as a private

contractor, lecturer, and author – and for this, I thank you very much.

Regards,

[-Richard Lyons-]

This time, the professor replied to me the same day(!) with:

Date: Thu, 10 Dec 1998 18:37:00

To: rick lyons

From: the professor

Subject: Re: Thank You

Dear Richard:

Digital Signal Processing”. …I am glad this has worked out

very well for you. However, I am one of those sensitive people

who goes out of his way to try not to offend others, so I would

like to clarify the situation of some years back.

At the time you contacted me, I was swamped with work and was not

in a position to revamp the DSP book. I definitely remember having

several conversations with you and receiving the material you sent

(which has never gone any further than my office). If I failed to

respond to you, please accept my apologies since there certainly

no intent to be insensitive to you. My failure to respond was

simply a “statement” that I was not in a position at the time to

do any more work in the area.

Again, accept my apologies, and congratulations on what sounds

like an excellent career move!

Sincerely,

The professor’s reply was fairly gracious, I must say.

To the professor, I must confess, I painted an overly-rosy picture of the situation in which I found myself after resigning from my full-time aerospace job in 1998. Indeed, all I had to do to survive after my resignation was not buy anything, not go anywhere, have no hobbies or personal life, and accept Government cheese to eat.

Rick Lyons

________________________________

Charan’s comment: Rick has just published his third book:

This is a great book for rank beginners and all high school students. It succeeds in explaining DSP WITHOUT equations! Got kids, siblings, you want to introduce to DSP, start here.

### 6 Comments on “Why I Wrote My “Understanding Digital Signal Processing” Book”

1. Arthur Dent says:

This was a fun read — thanks for posting it. On Richard’s advice I’m going to write a book on signal processing with massive amounts of the other topics mentioned 🙂

• Luis Sanchez says:

How can you mix DSP and the other topics? ha ha ha.

On a more serious note, Mr. Richard, congrats! I find your book very good! You explain the topics very well. It definitely honors the title.
congrats!
Luis.

2. MimS says:

Dear Rick;

I would like to thank you for your book and let you know that anything I understand in DSP, come from your book “Understanding DSP”,
really appreciate!!!.
Mehdi
From IRAN

3. russ ward says:

lyons “understanding dsp” book was good on dft but weak on fir –
57 page chapter of dsp tricks could have been better spent –