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I did implement the viznut waveforms for the VIC-20. It was full of nasty surprises for sure, given the difficulty of making well timed 6502 code (added cycles here and there depending on code/vars locations), and really lacking debug tools. Even worse, VICE has some weird audio filtering going on, and MAME does not support expanded RAM for VIC (5K default model only), so I was not able to hear the sound properly, and my test code didn't fit to run in MAME.

It worked in the end, however, it wasn't much suitable for music. The thing is that these waveforms always contains 8 zeroes and 8 ones, just arranged in different ways. So it can't do the usual 50-25-12-7 duty cycle, or arbitrary bit patterns of PET, it just adds high pitched harmonics into square wave. So a special arrangement for music is a must, that would mostly rely of square wave and emphasize some parts using waveforms.

Here is the key part of the code (waveform_table there is to attempt to arrange waveforms in order from regular bold square to the thinest one):

set_pitch_and_wave:

    pha    
    tya
    bne :+
    
    sta <PV_WAVE_PREV,x
    lda #$7e
    sta VIC20_LOW,x
    pla
    rts
:
    
    asl a
    tay
        
    lda waveform_table,y
    iny
    
    cmp PV_WAVE_PREV,x
    beq @skip_wave
    
    sta PV_WAVE_PREV,x
    sta PV_WAVE_PTN
    
    lda #$7e
    sta VIC20_LOW,x
    
    lda waveform_table,y
    
    ldy #100/5                ;delay t-states/5
:
    dey
    bne :-

    tay

@loop:

    lda <PV_WAVE_PTN        ;3
    and #$80                ;2
    ora wavecnt_table,x        ;4+
    sta VIC20_LOW,x            ;4+
    asl <PV_WAVE_PTN        ;5
    lda <PV_WAVE_PTN        ;3
    nop                        ;2
    nop                        ;2
    nop                        ;2
    dey                        ;2
    bne @loop                ;2/3=32t

@skip_wave:

    pla
    tay
    lda (PV_NOTE_TABLE),y
    sta VIC20_LOW,x
    
    rts

wavecnt_table:

    .byte $7d,$7b,$79
    
waveform_table:

    .byte %11000000,3    ;00
    .byte %10010000,6    ;14
    .byte %10100000,5    ;09
    .byte %10100000,4    ;12
    .byte %10110000,6    ;11
    .byte %10110000,5    ;07
    .byte %10000000,2    ;01
    .byte %10000000,3    ;04
    .byte %11010000,5    ;08
    .byte %10101000,6    ;13
    .byte %10010000,5    ;06
    .byte %11100000,4    ;03
    .byte %10110000,4    ;02
    .byte %11000000,5    ;10
    .byte %10000000,4    ;05
    .byte %00000000,0    ;15

In fact, I think I'll release the whole sound code sometime later. Released album code contains most of it anyways, it only missing VIC-20, C64 and NES dependent parts.

It is just matter of personal taste. There are dozens of popular trackers in the history that didn't follow the line. There are sequencers in the history that didn't display anything at all, yet was very handy to create music.

It is impossible to do with this design, anyways.

v0.31 is out. Many fixes in the front-end and many engines. Minimal examples and docs for each and every engine. The classic two-channel engine from Robin Hood is added, in all of its original glory.

My congratulations, utz, and Tufty, on stealing my imminent victory once again! Took me some time to figure out who is behind these amazing tracks, it wasn't too obvious this time, even though I did have clues that engines likely were used and your preferences.

I'm not a BK user, I think I've never seen one working, so I have about as much clues as you do. Even knowing Russian does not help much there, it all looks extremely cryptic.

Don't put your expectations high, this was only supported by hobbyists who just did their first steps in software development. What you can expect from a computer with a keyboard that looks like it came straight up from a cartoon? In fact I think it is part of the puzzle, it had a ton of cryptic named keys.

There is also BKBTL that has a Qt port and is supposedly works under Linux.

To be honest, I have no idea what the BIN format is, and where it comes from.

177716 has a lot of other stuff, ranging from tape controls to CPU reset vector (!). Don't forget, it is a 16-bit register with plenty a bits on a really oldschool architecture.

Here is a list of emulators for Windows. The list says there are better options, but I prefer to stick to one I'm most familiar with, Bashkiria-2M emulator (called just Emu).

So far I have found about 5 beeper editors, but was able to load and hear something from with only one, with a 3-channel engine, called Klavesin (attached).

How to get it started:

Start Emu
Select BK-0010_01
File/Open, set filter to all, select klaves.bin

All others are disk based ones, so you have to be a bit familiar with the MK-DOS on BK-0011, which looks much like Norton Commander from DOS era. Then it gets worse, as neither of the editors have a demo song loaded (but there are some on disks), it is all in Russian, and it considers you know something about the thing. So I wasn't able to figure out any of those yet. Seen that one has loadable 2-ch and 4-ch drivers and a few songs ripped from ZX Spectrum (judging by the filenames).

If you'll go the Nth/note with time signatures route, it will be not possible to properly support in tracker-alike editors (I had to replace such formats in some classic engines in 1tracker). Many also consider this format to be difficult to write by hand. So while it may have its own benefits, it dooms the format to never gain popularity.

Thanks to utz's input I got PET running in MAME. Turned out that MAME emulates 6522 quirks better, like, VICE would allow incorrect code to work just fine. However, MAME's SR produced pitch is twice higher than it should be.

I'm working with VICE, as I wasn't able to set up MAME properly. Judging by MAME source code, it does emulate IRQ on shifting, or trying to do so, at least. Latest updates to 6522 emulation there were doing in August, so it is kinda alive.

Emulation quality in VICE, on the other hand, is kinda questionable. It is incomplete, and the way the sound emulated is really weird. Like, direct CB2 control sounds unfiltered, while SR-driven sound is clearly filtered with very weird curve, it gets quieter as the pitch rises, up to the point of being really faint, then gets back to normal volume. So it sounds like a mess in a normal music. Also pitch and frame rate seem to be a bit off.

I didn't find any in-depth docs other than that you're mentioned, and I missed pet-io-2.txt altogether (thanks!). I also used 6522 datasheets, there is three of them, and they're actually different. Synertek SY6522 from 1982 (not 1978!) seem to be more detailed in the timers section. I also looked up VICE and MAME source code.

As I don't have access to the real thing, and active back-and-forth is kinda difficult to do (David is busy man), I can't say for sure. However, Synertek datasheet mentions it explicitly - first enable shifting, then load value to the register to start shifting. As for bit 5 of ACR and loading $ff, I did it other way, by toggling bit 5 of PCR - it does work on the HW regardless of the shift register contents. However, there is the missing notes issue, may be related to either of these things. Will try your approach (looks more elegant), thank for hints.

T2 high byte is not supposed to work in the free running mode. I hoped there is some hack to make it work, but considering not so precise emulation and lack of real hardware (not even sole 6522 chip) on my end, I can't do tests. Well, the main issue with pushing PET is that it isn't emulated well (not all timer modes covered, for one), and there is like 1.5 PET emulators around (.5 in MAME, difficult to setup).

To me it seem the only viable way at the moment is to use IRQ to toggle CB2, I did it as a software Shift Register imitation there. However, there is some issue on the real HW that is not figured out yet is that some tones disappear when you switching between IRQ and Shift Register (just on the transition point, maybe IRQs get skipped?), and this behavior is not emulated (works just fine in emulator).

Another issues are that default IRQ handler pushes all the registers before going IRQ trampoline, which wastes a ton of time; default system handler still need to be called once a frame (to make keyboard input work for the game), which introduces clicks; and unexpectedly annoying one, speaker in PET barely can reproduce low frequencies, they're getting very quiet.