[sdiy] Digital Waveshape Generator.

[Roman Sowa]

Isn't it how PPG Wave works, also Korg DDS-1 or DW8000? They surely used 
some clever tricks to push the envelope of then-available technology and 
didn't use simple division of high frequency clock. I navere serviced 
any of these so I can't tell. Not to mention DIY implementations. My DIY 
synth built with this concept in 1990's used only 8-bit dividers and 32 
byte wave memory and still sounded nice.

In your document you suggest using 1.8MHz clock and 12-bit dividers. So 
with 256-byte wave, the top note you can get will be just 2Hz. That 
really needs faster clocks. You were correct in 1981 about hundreds of 
MHz. Or should I say a glimpse of GHz. The divisors you proposed are way 
too high. Commonly used dividers in top octave organ chips use 9-bit 
numbers only, and were used with great success in milions of instruments.

But still you can use PLL after the divider to have low frequency master 
clock (like 4MHz), old organ TOG dividers, and then x256 PLL to drive 
RAM counter.

Roman



W dniu 2025-07-11 o 21:19, Phillip Harbison pisze:
>
>
>
>
> 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.
>
>
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