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The idea above gives this simple PWM modulation type for the 16-bit adders system. It takes two 16-bit accumulators but a single adder:

    ld hl,0 ;acc1
    ld de,0 ;acc2
    ld bc,100 ;adder
    
loop

    add hl,bc
    ld a,h
    inc de
    cp d
    sbc a,a
    and 16
    out (#fe),a

    jp loop

Yeah, I trying to get my head around it, but it doesn't really works the expected way. The inner adder works as usual, 3500000/t-states of inner loop/(65536/FREQ1). The outer adder is presumably 3500000*number of inner loop iterations/t-states of inner loop/(65536/FREQ2). However, when the second (modulation) frequency happens to be above the inner loop sample rate, i.e. a few phase changes should happen, it introduces another frequency into the equation, a kind of low frequency carrier, and the resulting frequency kinda gets unpredictable.

Not that it is useless anyways, but to make it usable from composer standpoint it is better to find a way to provide the secondary divider in a form better than a 0..65535 value per note.

One problem with it is that I still can't figure out the math required to control the modulation in a predictable way - without it a suitable modulator needs to be hand picked for each and every note. So yeah, maybe a variable rate offset will turn it into something more useful and controllable.

I'm not sure if we ever used it somewhere, sometimes I'm forgetting all the tricks we've discovered prior. Anyways, a weird kind of modulation:

 add hl,bc
 ld a,h
 cp duty
 sbc a,a
 out (#fe),a
 ... 256 times

 each frame:

 ld de,1000
 add hl,de

I.e. each frame add another value to the accumulator. Different values produce various kinds of modulation, a good variety of those.

Complete results yet to come, as the prizegiving is going right at the moment, but congrats, AtariTufty (2nd with Synthetic Heartbeat) and utz (1st with A Strange Game)! Finally, utz's entry got a praise it deserves! My personal favorite this time was AER's Cosmic Puppy, though.

Color me impressed, guys! 7 songs, and the humble beeper is still at rise! So many cool sound colors, so many neat finds. The compo is still kinda crowded with my engines, tho. Sorry, was busy, had no time to add the recent utz's developments to the tracker yet, but I believe some of those are the next best picks.

Great! I thought of eliminating the row noise as an obvious engine evolution step to take, but never really done any engine with that.

A note, the tables for the data structures in the docs are messed up for Pulsatilla and Pindsvin. Not really sure how interpret them at the moment, Pulsatilla's table somehow mention ch5 even.

Pretty cool, dynamic tune. Guess it is time to put some work into a Phaser4.

This is kind of an answer of the Soviet electronics to the graph calculators such as Ti-8x. To my knowledge, it is a totally unique design, not a copy or derivative of something (like most of other Soviet electronics), yet it is based on the cloned CPU architecture, yeah - the 16-bit LSI-11, which is at heart of the BK line of home computers. It even had a dock station MK-92 with a 4-color plotter and tape interface. First prototyped in 1986, released in 1988, produced till 1992. At the time of release it used to cost nearly as much as a small Soviet car. Not a vapor hardware either, I personally seen it in a shop being a kid.

It was the last mass produced device of such kind in the USSR. There was a similar but 8086-powered MK-98 follow up in the works, a few production quality fully functional prototypes were found, but it was never available to the mass market.