[sdiy] Digital Waveshape Generator.

[brianw]

It would seem that Hal Chamberlin has you all beat. His masters thesis, circa 1973, was a digital waveform synthesis engine like what has been described. I attended North Carolina State University from 1984 to 1988 and was building such things on wire-wrap peripheral cards for my Apple ][. After learning about Hal Chamberlin, I visited the library stacks and found the physical copy of his thesis from the early seventies, and it was almost depressing that I couldn't think of anything newer. So far, that thesis is not available in digital format except for a few isolated pages (used in patent documentation).

I still think yours is a worthwhile project to pursue, although it probably would not be a commercially successful product. I also think it's worthwhile to pursue in discrete logic, rather than software. I have done both, and hardware has its advantages. As Richie Burnett has pointed out, there are advantages to using dividers so that each voice can have its own hardware sample rate as a whole multiple of the number of samples.

As for the sample rates, 44.1 kHz is fine for digital media as a final delivery format, but recording usually benefits from higher sample rates - even if the final mastering decimates to a lower sample rate and bit depth. For synthesis, I imagine that very high sample rates can be beneficial, and that would be true even if the analog output of the synth were recorded at lower sample rates. Impulse responses and phase accuracy would have finer control with higher sample rates and fewer sample data calculations.

Brian

p.s. What year did you start your design? I am also a fan of Larry Fast / Synergy, so it really brings back memories of my own hardware synthesizers and samplers that I built in the eighties. I read a great many synthesis articles in PAiA Magazine and the followup publications.


On Jul 11, 2025, at 2:06 PM, grant musictechnologiesgroup.com wrote:
> 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
> Date 7/11/2025 1:12:23 PM
> 
>> 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
>