[sdiy] Digital Waveshape Generator.

[The SynthiMuse]

Hi Phil

I enjoyed your email.
At roughly the same time as you were building your DWG, i was working on my
trade college project that was a digital sampler. It used a programmable
divider like your design. We could easily have combined our projects and
conquered the 1980's synth world! 🙂

If you're interested in going down the coding route, Tom Wiltshire's
Electric Druid VCDCO design is really nice and understandable.

https://electricdruid.net/product/vcdo-wavetable-oscillator/

It's a phase accumulator design rather than a master oscillator that's
driven at different frequencies.

Another good read is the dataset for the AD9850 Direct Digital Synthesis
chip.

https://www.analog.com/en/products/ad9850.html

EBay have cheapo clones of this chip mounted on pcbs and ready to play with.
I don't think they have waveform memory but good for learning the
principles of DDS

I hope you find this all interesting.

Best Wishes

Gerry Murray


On Fri, 11 Jul 2025, 20:24 Phillip Harbison, <alvitar at xavax.com> wrote:

>
>
>
>
> 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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