[sdiy] Digital Waveshape Generator.

[Phillip Harbison]

Hello, Synth-DIY people. I'm a long time listener but infrequent poster. 
The following has been on my mind and IO would appreciate your opinions.

I graduated from the University of Alabama in Huntsville (UAH) in 1981 
with a degree in Electrical Engineering. For my senior design project I 
designed and implemented what I called a Digital Waveshape Generator 
(DWG). I intended this DWG to be the core of a single voice in a 
synthesizer. A block diagram and design document are attached.

I had a strong interest in music synthesizers as I was a trained 
classical pianist and a fan of progressive rock music. For most of high 
school I dreamed of being the next Rick Wakeman or Larry Fast, but I did 
not have the necessary gear. I intended to build my own, but after 
graduation I was to busy with Real Life to work on toys.

One reason I lost interest is at the time I thought the master clock 
frequency needed to be 256 times the least common multiple of the 12 
notes of the top octave. I don't recall how I calculated it, but I 
thought I needed a clock in the hundreds of megahertz and in 1980 the 
only technology capable of handling such frequencies was ECL, That was 
not happening on a poor student's budget. I still got an A+ because my 
advisor did not give a damn if my DWG was musical. He saw it simply as a 
cool function generator.

Now that I am semi-retired I revisited my design and the first thing I 
did was realize that I was wrong about the master clock frequency. For 
one thing, there is no Least Common Multiple possible since 11 out of 12 
notes are not integers. I also realized I don't need to find divisors 
that will produce the exact frequency of each note. Getting within a few 
cents would be close enough for rock & roll. After a lot of calculating 
I determined that a 1802240 clock and a 16-bit divisor would allow me to 
generate all notes of the top octave within 0.02% of perfect.

My prototype was wire-wrapped. Now I am wondering if I should create 
some circuit boards and realize my dream of a DIY digital synthesizer. 
Is this something anyone else would find interesting? Am I wasting my 
time? I would appreciate any comments.

-- 
Phil Harbison

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