[sdiy] Digital Waveshape Generator.

[Chris McDowell]

Hey Phil, 

Definitely fun and interesting, I'd love to follow along if you go down this road. 

I think folks will chime in with a lot of input on your strategy. My gut immediately says there are very good ways to do this without all of the hardware digital logic (depends on your goal, of course). 

There are a handful of write-ups floating around about the Juno series that have good info (that generally agree with your assumptions) on generating the digital ramps from a shared clock. The Junos were only worried about the period, not with having a full 256 counts to address RAM, but it's relevant and worth looking at. 

To your last question "Am I wasting my time?", eh, "waste" is a strong word because designing systems is fun. If you were trying to make this into a product in 2025, I think you'd pick a fast microcontroller and do all of this monkey business in code, accepting the tradeoffs we're all familiar with. 

Cheers,
Chris McDowell 

> On Jul 11, 2025, at 2:19 PM, Phillip Harbison <alvitar at xavax.com> wrote:
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> 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.
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> 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.
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> 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.
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> 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
> 
> <DWG_BlockDiagram.jpg><DWG_Design.pdf>________________________________________________________
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