> On Jul 11, 2023, at 7:43 AM, [email protected] steven--- via cctalk
> <[email protected]> wrote:
>
>> On 07/10/2023 11:31 PM AEST Mike Katz via cctalk <[email protected]>
>> wrote:
>> Way back in the 80's I was able to do stereo 4 part harmony on a 2 MHZ
>> 6809 using two 8-bit D/A converters.
>
> Much the same here. I recounted this on VCFed a few months ago about building
> a simple 2-chip 8-bit ladder DAC with one-transistor amplifier for my Applied
> Technology DG680 S100 machine back in the early 80s from this absolutely
> excellent BYTE article on how to do polyphonic synthesis on a microcomputer
> (KIM-1):
>
> https://archive.org/details/byte-magazine-1977-09/page/n63/mode/2up
>
> A schoolfriend who had an Apple ][ and had not done any Z80 machine code
> before asked for me to hand him my Zaks book, upon which he wrote out one
> attempt in Z80, crossed it out and wrote a second version. Which worked
> perfectly. For the music piece I got it to play four-voice polyphony after
> painstakingly encoding Bach's Praeludium in C Major from my mothers'
> collection of piano music scores.
>
> A few years ago I had thoughts about porting the 6502 code to the PDP-11 and
> use the same sort of ladder DAC. Not sure if the slimline 11/05 would be fast
> enough for anything too high frequency, but if it was, the slimline 05's
> power supply could then temporarily come out and be perhaps be powered off
> some beefy batteries in that space, along with a small 1970s transistor amp
> and 1970s headphones topped off with a leather shoulder strap to lug it
> around like a giant Walkman.
Speaking of old computerized music playing technology, there are two from the
PLATO system at the University of Illinois that are perhaps the earliest of all
in their category and not all that well known.
The first of the two is the GSW (Gooch Synthetic Woodwind), which is a four
voice, 7 levels per voice, square wave synthesizer. It's fully documented in
Sherwin's US patent 4,206,675. That one was attached to the auxiliary device
port of a PLATO terminal and driven from the host computer, at 1200 bps. It
worked quite well for playing music and was widely used for music education.
It's a very simple device as you can see from the full schematics (which are,
surprisingly, given in the patent). That patent was filed in 1977 but the
invention is somewhat older, perhaps 1975 or 1976.
The followon to that is the GCS (Gooch Cybernetic Synthesizer), unfortunately
not well documented. That's a 16 voice programmable waveform (256 words by 16
bits per voice), more levels (256?), driven as a peripheral off the 8080-based
"programmable PLATO terminal" from a program running in that terminal. So the
musical score level definition of what to play still came from the host, still
at 1200 bps, but the attack/decay etc. shaping would happen in the terminal.
That one was a bit of an electrical muddle, with memory, logic, and D/A per
voice followed by a 16 input combiner. Getting the analog parts to work right
was a hairy task with far too many trimpots. Sherwin vowed that any followup
would be digital all the way to one final D/A, which of course later became the
answer in the PC sound cards, but if he did that it was after I left. The GCS
was built around 1977. There were some interesting related pieces of work,
such as a speed-sensing piano keyboard (so unlike an electronic organ you could
have dynamics, exactly as on a piano), a music editing system with a score
printing program to print on a dot matric (electrostatic) printer, and some
other stuff.
I'm not sure if the GCS is the earliest fully programmable waveform digital
music synthesizer, but if not it is close.
paul
