[sdiy] Digital Waveshape Generator.

[grant musictechnologiesgroup.com]

Funny. At about the same time I was working on a 6809 based digital sequencer for the horrible Roland SH-3a synth and my lab partner quickly sketched out a wavetable synth on the back of a Decwriter paper terminal page from the mainframe.

http://www.musictechnologiesgroup.com/images/GregsWaveTable.jpg

Flip the image over to see the era.

I guess we all missed out...

GB


------ Original Message ------
From "The SynthiMuse via Synth-diy" <Synth-diy at synth-diy.org<mailto:Synth-diy at synth-diy.org>>
To "Phillip Harbison" <alvitar at xavax.com<mailto:alvitar at xavax.com>>
Cc "synth-diy" <Synth-diy at synth-diy.org<mailto:Synth-diy at synth-diy.org>>
Date 7/11/2025 1:12:23 PM
Subject Re: [sdiy] Digital Waveshape Generator.

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<mailto: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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