226 Reply by Shiru

(13 replies, posted in Other Platforms)

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.

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227 Reply by Shiru

(13 replies, posted in Other Platforms)

6522 is not a real serial interface, it is merely a timer plus shift register, so it does not really know about start and stop bits, it is all up to software to implement actual communication protocols.

When 6522 used for CB2 sound, the free running mode driven by T2 counter is used, that is, a 8-bit counter divides 0.5 MHz and clocks a 8-bit output shift register that is looped. Naive approach for PET sound is to load %11110000, %11001100, or %10101010 into the shift register, then set up T2 counter to some desired frequency. This means you can't go below 500000/255 Hz (~245), but you can have wave shapes other than regular square wave.

There is another mode where you can also output an arbitrary bit stream, getting an IRQ every time when shift register gets empty, thus getting some buffered playback. This mode is not emulated, unfortunately.

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228 Reply by Shiru

(13 replies, posted in Other Platforms)

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.

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229 Reply by Shiru

(13 replies, posted in Other Platforms)

I liked the achievement, but the bit pointed at Mr. Murray was kinda uncool. The 'wrong' person 'hired' implied there is me, I'm working on sound code for his project. Not to mention it questions my abilities, it also does not consider Mr. Murray has a vision on what he wants in his project. Sure I proposed multichannel stuff, sampled SFX, and other advanced things a while back for Planet X3, and once again for this one, but these ideas were all rejected in favor of the standard monophonic sound, not even going below the 245 Hz limit was considered at first. It also needs to be cross-platform (VIC-20, C64, with their native sound as well), and fit into mere 2.5K with code, SFX, and a music track.

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230 Reply by Shiru

(166 replies, posted in Sinclair)

I don't think I did anything that would break this compatibility. It is an SDL2 app, maybe something happened with the lib in lastest updates. Will check it out sometime later, thanks for report.

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231 Reply by Shiru

(166 replies, posted in Sinclair)

Yeah, by some reason SDL designers decided to not go in order, like ASCII or VK codes, and I didn't notice it.

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232 Reply by Shiru

(166 replies, posted in Sinclair)

Thanks for report. Turned out there is a metric ton of various issues in the v0.3 release, working on fixing them for a while now.

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233 Reply by Shiru

(8 replies, posted in Sinclair)

At the moment we have plenty engines with wavetable and sample playing capabilities.

utz did a great range of wavetable engines that using 256-byte long looped samples, which is enough to represent vowels; I did a number of engines with sample-based percussion of various kinds.

Just a few days ago I released SquatE, which is very close to your Squeeker (thanks a ton for this thing!), plus it features a sample channel that plays along without interrupting the tone channels. This was done exactly with vocal and pitched instrumental samples in mind. It can be done even better, as a song with vocal parts would need good compression, and 1-bit samples seem to be compressible with basic RLE well enough, so the next step would be an engine with on-fly RLE sample decoder, and a wider number of samples (currently numbers limited to 7-15). Perhaps with a sample offset effect, even.

As for a real-time vowel synth, I think we're discussed this possibility at some point somewhere around here. This sure yet to be done.

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234 Reply by Shiru

(5 replies, posted in Sinclair)

That's nice, please remind me if there are major issues with tracker or engines, maybe I'll get another round of updates to fix (some of) them.

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235 Topic by Shiru

(5 replies, posted in Sinclair)

An updated version of my older Squat engine. It features much higher sample quality, achieved by using interleaving mixing technique in the Music Box fashion, as well as reading two samples per one iteration of the tone loop, so while tone channels update at ~8400 Hz, sample channel gets updated at ~16.8 KHz, and they're not getting masked by the tone channels anymore. Strategic timings applied to even out tone and sample volumes. This helped to make samples sound much clearer, now suitable for high-frequency instruments such as hats, and for tonal instruments, to some extent. New mixing scheme affected the way tone channels sounds, too, so it does not obsolete the older version, they're more like two flavors of the same thing (gritty loud sound vs clean, but thinner one).

- 4 channels of tone, each channel has its own duty cycle
- Noise mode for the last tone channel
- Noise percussion, 9 pitches of noise at 4 volumes
- 15 non-interrupting sampled drums, can be very lengthy
- Improved speed range

Like usual, it is included into the latest 1tracker release.

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236 Reply by Shiru

(2 replies, posted in Sinclair)

Relistened it again. Damn, such a great song and sound.

I recall I didn't recognize my own engine here when I heard it for first time. Yet another example that you never really realize true limits of your creation(s). Happened with Tritone and Octode engines in the past as well, even though I was able to recognize them, but was surprised by what composer guys managed to pull out of those.

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237 Reply by Shiru

(166 replies, posted in Sinclair)

A minor update to v0.3, libs updated, some issues fixed, SquatE added. Windows x64 build introduced.

There is an unofficial fork of Game_Music_Emu that is still maintained. However, I ran into a weird issue with it that it works properly only in Debug build, but glitches all around in Release (mostly cuts playing after a very short while). Wasn't able to figure it out, so I decided to stick to the latest official version, even though it is kinda old.

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238 Reply by Shiru

(166 replies, posted in Sinclair)

Sure, but this is done on per-engine basis, so no quick fix. Some engines do break long lines, while others (Tritone Digi?) not. Will handle this a bit later.

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239 Reply by Shiru

(12 replies, posted in General Discussion)

All Tritone songs before Beepola were made with the XM converter. Some of them still made with the converter, because it gives the super speed capability (to imitate arpeggios and slides).

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240 Reply by Shiru

(35 replies, posted in Other Platforms)

A ton of distractions happened since, but English translation of the making of the demo is finally here: https://habr.com/ru/post/486010/

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241 Reply by Shiru

(43 replies, posted in Other Platforms)

I'm not much familiar with the Savage code, and it is super convoluted to figure it out at quick glance, but it looks like it relies to IM2 handler a lot. Simply removing it certainly won't work. The engine can be rewritten (recreated) to work without interrupts, I think, but it is more like making a new engine from scratch than a simple edit.

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242 Reply by Shiru

(5 replies, posted in Other Platforms)

Now not 1-bit, but ZX Spectrum related - I made a PT3 player (with AY emulation) that plays files loaded into the internal memory. Cool thing about ESP8266 is that you can load these files over Wi-Fi. Forum thread.

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243 Reply by Shiru

(5 replies, posted in Other Platforms)

As a first step, I ported over my PC Speaker album System Beeps. Due to the nature of the platform it comes in form of source code (for regular Arduino IDE). More info on the official forum.

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244 Topic by Shiru

(5 replies, posted in Other Platforms)

ESPboy is an open source DIY handheld, kind of Arduboy, but powered with 32-bit ESP8266, and with a color screen. For sound it only features 1-bit piezo on the board (maybe will be replaced with a tiny speaker in further revisions), controlled via GPIO line. The creator of the thing asked me to help with the sound code, his intent is to bring ZX Spectrum beeper music to the platform. So I'll be porting some engines (Phaser1 is ported as proof of concept at the moment). Thought it may be interesting to some folks here.

More info on the device:

https://hackaday.io/project/164830-espb … cation-fun
http://community.espboy.com/

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245 Reply by Shiru

(1 replies, posted in Sinclair)

I'm pretty sure that ZOSYA is in fact Oleg Origin undercover (and it is not clear whether he is really an actual person, too). Oleg is known for disassembling a good amount of better classic engines back in 2012, such as Trantor and Dark Fusion, as well as making a few new ones, but he never released the source to those. Sounds much like one of the latter.

Not BuzzKick for sure.

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246 Reply by Shiru

(5 replies, posted in Sinclair)

Sounds legit, would be at home in a pre-1985 ZX game.

You don't really need to hand tune pitch values, just use any script engine to calculate them out. JS, Python, etc.

Then, if you go with composing by typing in the pitch values, you don't have to have a spreadsheet. Just make aliases, like C_2=100 (or C_2 equ 100 in some assemblers). Now you can just use note names in your db's.

Then, to save time, you can just generate both pitch values and aliases with the same script, and save a ton of time. You can do this with https://js.do/, for example. Just go there, copy/paste code below, click Run.

<script>

    //standart note table for a high octave

    NoteFreqTable=new Array( 2093.0,2217.4,2349.2,2489.0,2637.0,2793.8,2960.0,3136.0,3322.4,3520.0,3729.2,3951.0 );

    NoteNameTable=new Array("C_","Cs","D_","Ds","E_","F_","Fs","G_","Gs","A_","As","B_");
    
    //generate note to period table

    cpuClock=3500000.0;
    cpuToneLoop=200.0;    //cycles per engine loop
    div=32.0;

    for(octave=0;octave<8;++octave)
    {
        for(note=0;note<12;++note)
        {
            period=Math.floor((cpuClock/(cpuToneLoop/2.0))/(NoteFreqTable[note]/div));

            document.write(NoteNameTable[note]+octave+" equ "+period+"<br>");
        }

        div=div/2;
    }

</script>

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247 Reply by Shiru

(21 replies, posted in Sinclair)

Did a small song using actual wtbeep engine, for CAFe 2019: https://soundcloud.com/shiru1bit/falling-asleep

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248 Reply by Shiru

(135 replies, posted in Sinclair)

The super fine volume/duty effect is certainly real and can be used, that's what I was referring to as having potential (will do something in this regard a bit later).

As for harmonics, yes, I suspect most of it comes from the downsampling filter in emulators, seems to be some unwanted oscillation at high frequencies. Still not clear if there is more to it.

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249 Reply by Shiru

(135 replies, posted in Sinclair)

Yeah, seems this technique has potential that is worth to explore further.

For now, the same thing with two channels and slides, demonstrates tons of harmonics.

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250 Reply by Shiru

(135 replies, posted in Sinclair)

I suspect I'm actually rehashing some old idea, just been experimenting with the phase shift to control volumes yet again. This snippet produces interesting harmonics as the volume rises very smoothly:

    ld hl,0
    ld bc,1200    ;frequency
    ld ix,0
    ld a,0
    
loop1
    ld d,0
loop

    add hl,bc
    jp nc,$+5
    xor 16
    add ix,bc
    jp nc,$+4
    xor a
    
    out (#fe),a
    
    inc d
    jp nz,loop
    
    inc hl   ;slowly increase the volume
    
    jp loop

Volume control here is made of two 16-bit adders that get the same 16-bit value added (3 register pairs per oscillator). The first one inverts the phase, the second one resets it. Volume controlled by the distance between initial values of the adders.

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