A 48Khz digital music player for the Commodore 64

https://brokenbytes.blogspot.com/2018/03/a-48khz-digital-music-player-for.html

by SwellJoe • 8 years ago

203 57 8 years ago

brokenbytes.blogspot.com

ainiriand• 8 years ago

Impressive piece of software building on the already impressive technique to play 8-bit that Mahoney invented.

A good moment to remember https://github.com/marioballano/emudore so I can experiment with this thing on the weekend.

vardump6• 8 years ago

Correct me if I'm wrong, but this doesn't seem to use Mahoney technique, it's just doing the plain old technique of writing SID volume register at 0xd418:

  l:      nop                 
  sample: ldx $8400 + i*$100  
          ldy $8000,x  
          lda sidtable,y   
          sta $d418      
          inc sample +1        
          bit $ea               
          ldy $8100,x          
          lda sidtable,y   
          sta $d418            
          inc $d020

...

popmilo2• 8 years ago

It is based on Mahoney technique. Achievement is in added decompression routine that works in those 21 cycles per sample. Lot's of cool info in that article. Nicely done !

Sharlin• 8 years ago

Wow. Remember that this on a machine that isn't actually designed to play digitized sound at all! (Though ways to hack the chip to do just that have certainly existed for a while, as mentioned in the article.)

Medox• 8 years ago

makes you wonder what our current machines could be doing in 20-30 years, that was not intended. Maybe some quantum emulation.

jacobush• 8 years ago

if anyone cared

simias• 8 years ago

The massive complexity, diversity and general black-box nature of modern PCs leads me to believe that we won't have a similar scene of enthusiasts to develop amazing hacks for, say, 2009 Dell Inspiron laptops.

There's an elegant simplicity in these old pieces of hardware, it's relatively easy to study them exhaustively and if you're clever enough you might find a new way to fit the pieces of the puzzle to do something nobody had though possible before. If you want to hack a modern PC you'll probably first have to spend a few years reverse-engineering the various parts to figure out how they work exactly and what you can do with them. Even getting a basic understanding of the low level details of a modern GPU is quite a massive undertaking.

harel4• 8 years ago

If Commodore (the company) had a fraction of the dedication and ingenuity of today's Commodore users we'd all be using their machines still, and reading about Apple enthusiasts who managed to squeeze another ounce of juice off their old Macintosh, or some fringe PC zealots who got their XT to display a different shade of green.

pgeorgi2• 8 years ago

some fringe PC zealots who got their XT to display a different shade of green

http://8088mph.blogspot.de/2015/04/cga-in-1024-colors-new-mo...

harel4• 8 years ago

Of course they did :)

cromwellian5• 8 years ago

The thing about the VIC II and SID is that they have just enough flexibility by exploiting the HW to pull off an astonishing number of effects, like stretching sprites/screen/characters by tricking the VIC to redisplay lines, this allows cool HW scaling effects. Or getting the VIC to delay displaying lines, which allows shifting the screen by more than 8 pixels in vertical and horizontal directions (the scroll registers normally only allow 8 different pixel positions)

People have exploited interlacing/sub pixel/NTSC/PAL effects to generate new colors, or simulate hi-res. They've combined changing color palettes per-line with sprite overlays to breach the barrier of 4 unique colors per 4x8 pixel block.

The list of surprising effects I've seen on the C64 never seems to end. Some crazy people have also managed to get the C128's VDC to do demo-scene effects as well.

One trick I was working on in the 80s before I quit the C64/C128 to go to the Amiga was to try and use the C128's MMU chip to run high speed 8502 code. The C128 MMU could remap the 0 page addresses ($00-$FF) into other memory regions. Because 0-page instructions run faster (e.g. STA $C000 vs STA $C0), if you could remap zero page, you could write code in a style that is significantly faster.

I wanted to use this to write a fast line drawing/poly-filing routine. Since the VIC could also be remapped by the MMU, in theory (I never go to to test it), you could map the zero page to a VIC mapped address, and do pixel block operations at 2-3 cycles per write.

harel4• 8 years ago

Hat off to you sir. I learned programming on the Vic20 (my first computer) and I still cannot surpass the level of excitement it got me then. I didn't dream to squeeze the hardware back then, I just accepted it and used a tiny amount of it. What I see done now is nothing short of amazing. If these talents of optimisations would apply to modern hardware, we wouldn't need modern hardware.

exikyut• 8 years ago

I wonder if anyone else has tried that. Ever tried poking that idea in the general direction of some demosceners?

bitwize3• 8 years ago

The PC was in some sense doomed to win. It is the natural successor of the S-100 bus. Commodore people have a hardon for "custom chips", exotic proprietary hardware soldered onto the mainboard in a special snowflake of holistic system design but what the PC provided was an open backplane allowing compatible systems to be built and integrated using parts from a variety of vendors. This gave the PC agility that even the best-managed company in the world couldn't match. It wasn't IBM's superior management that put the PC over the top, it was the combined forces of Dell, HP, Gateway, Tandy, and all the little peripheral vendors, to say nothing of Taiwanese white-box builders.

And in addition to the 8088MPH demo mentioned downthread, MDA graphical demos should in principle be possible by rapidly changing character RAM as the beam passes by. This is a trick I saw to generate graphics on another text-only monochrome machine, from Commodore: the PET.

harel4• 8 years ago

OK, lets assume Commodore's chips would have become the intel equivalent, and an open standard. They could have easily been the PC if they went the same way. It's not far fetched, just mismanaged. They could have done it and gone there but they didn't have the vision. And don't get me wrong, I'm not complaining or have regrets. I enjoy my Linux laptop and I couldn't care less if it's an intel chip or commodore that drives it. But I do know that one of them triggered excitement and one is just "a chip". Maybe it's my age, maybe its nostalgic memories of an era. I don't know... (can you run linux on commodore??? now that would be something...)

mnx• 8 years ago

where do the visual effects (those blinking bars) come from? Are they deliberate, or some sort of side effect?

vardump6• 8 years ago

They're deliberate, done by incrementing border color register. One of the only things possible with the available CPU time.

tonysavon6• 8 years ago

The three-byte codebook version (the mazinger demo) can't even afford the increment, and just does a sty $d020, which takes 2 cycles less, hence the colorbars look a bit different on that one. But the audio sounds better.

csixty4• 8 years ago

They're raster lines. At some point in the code, or multiple points, the program increments the register holding the border color so the video chip starts drawing a different color. This can happen in the middle of a line, which is why you get multiple "columns".

Edit: vardump is right, the screen would be "turned off" in this case so just the border color is used. This gives a slight performance boost.

pgeorgi2• 8 years ago

You get a bit more speed out of the C64 if you disable parts of the video chip. It also avoids cycle inconsistencies every 8 scanlines (where normally, the chip would block the bus for an additional cycle).

To avoid making it a dull monochrome screen, devs tend to push the data that they process into the border color register (acting as background color in this mode). You also see this with decompressors at the beginning of (cracked) games. So the background color gets updated every few multiple of 8 pixels (1 character), and there's where the patterns come from. The slow shift of the pattern to the left indicates that the code isn't entirely balanced, but the article states as much (is it moving every 1.28 secs? I can't tell).

sp332• 8 years ago

Yes, it does jump every 1.28 seconds :)

cromwellian5• 8 years ago

If you think that’s impressive, look at the demos thealgorithm pulls off On a stock c64 with no expansion. Advance to the 11minute mark: full screen streaming video and audio from a floppy

https://youtu.be/FTtKHLZTbtA

He also has a 22khz demo that plays back a full song on stock HW.

Seeing full screen video and audio on an 8-bit machine in 1982 would have seemed like alien technology, it would have blown people away. Years later people would be impressive by simple black and white QuickTime movies on far more expensive and faster HW.

neotek• 8 years ago

Way better source video:

https://www.youtube.com/watch?v=yW5v93P-gBw

cromwellian5• 8 years ago

I deliberately put the low quality one because it has the crowd reaction included at the demo contest, and I really enjoyed the crowd losing their shit when the full screen video + audio came on. :)

I just noticed he compressed an entire bananarama music video with better quality sound into a 1Mb REU.

https://www.youtube.com/watch?v=xH3yrLG8K7g

tonysavon6• 8 years ago

This is on stock C64 too :-). I guess the achievement here is using compression at such a high frequency. Once you get down to lower frequency, you can implement fancier compression schemes and add more stuff on display. The same author has compressed video plus compressed digi streaming from floppy disk here: https://www.youtube.com/watch?v=qIRww2a59lE But of course, that's not 48Khz and it sounds like that :-)

dzdt• 8 years ago

Not really. Stock C64 plus 1mb cartridge.

The big innovation was Pex's discovery of a way to output 8 bit samples by a single register write on the SID chip. The chip was never designed for outputing digital samples, and the approach leverages basically a bug in the chip design to achieve this.

The only innovative bit in this new demo (besides presuming to use a cartridge for storage) is the vector quantized compression technique.

onnoonno• 8 years ago

Even more impressive are IMO the current songs people compose on the SID. This guy is an artist in the true sense:

https://www.youtube.com/watch?v=ELpnGDHo0Bg https://www.youtube.com/watch?v=eI5d6Y0Fzl4

Yes that is 100% original C64, no extensions, no cartridges. The first time I heard these, I was absolutely blown away.

bsdhacker• 8 years ago

This is even better: https://youtu.be/bIM4p0uL6Pw?t=453

jdalgetty• 8 years ago

Imagine hearing that in 1982

squarefoot• 8 years ago

Sound could be produced by PWMing an i/o port to an integrator, so no need for the SID, and PWM could be generated through a register loaded with the desired value then decremented setting that pin to a 1/0 ratio according to its value, that is, turning the value into a duty cycle which once fed into the integrator becomes a voltage. It's simple in theory, but being the parallel byte serialized into essentially a single bit that would require some speed the 6502 could hardly be capable of.

tonysavon6• 8 years ago

Playlist with the three demos:

https://www.youtube.com/playlist?list=PLFeDsJqcV6DhwH16fVp_a...

js2• 8 years ago

You could never do this on an Apple II. The Apple II hardware was limited to a one-bit click of the speaker (in part due to a dispute between Apple Computer and Apple Records?).

But there was a modem for the Apple II, the Novation Apple-Cat II that contained a tone synthesizer and could be used to play music out over the line. To this day, I think that modem is one of the neatest peripherals ever made:

http://www.jammed.com/~jwa/Machines/cat/

Someone• 8 years ago

You’ll be surprised how far one can push that. https://www.kansasfest.org/wp-content/uploads/Beyond-the-Bee... mentions 22 kHz sounds, http://eightbitsoundandfury.ld8.org/software.html even mentions 44 kHz.

It references SAM, a software speech synthesizer that could run on that one-bit click speaker (“with the addition of much distortion”, as Wikipedia says)

dfox• 8 years ago

For what it's worth in early 90's people were playing PCM audio on PC speaker, which is single bit DAC that is in turn controlled by programmable interval counter and thus effectively cannot even directly produce single bit PCM. Norton Commander (5 or so) even included PC-speaker WAV player.

Edit: also having only one bit can be offset by larger sampling rate. In fact this is how probably every non-audiophile audio DAC manufactured in last 25 years works.

dep_b• 8 years ago

I wasn't expecting to be blown away by what they could do with the SID chip last time let alone now. Could you use the C64 as a hi-fi sampler with an analog filter or it's not possible anymore to use the LPF?

coin• 8 years ago

I wish people would learn how to abbreviate the units correctly. Hertz is abbreviated as "Hz". The kilo prefix is "k". Thus kilohertz is "kHz" and not Khz.

mrguyorama2• 8 years ago

Everyone seems entranced by "wow this would have been cool in the 80s", but the compression is a necessary part of the puzzle. How fast could you do k means clustering on 80s hardware?

tonysavon6• 8 years ago

That's a very good point! And also one to keep in mind for a possible additional demo. Use only hardware from the 80s also for the encoding!

mrguyorama2• 8 years ago

I think the demo is still really cool. I mean more to push back against the "programmers are lazy look what you can do with limited resources" ignoring the fact that the limited resources were only used for the playback part. Still awesome, just not possible in the 80s

ekimekim• 8 years ago

Very cool! I did something similar for the Game Boy Color recently - playing 18kHz ~7bit audio while also updating the screen at 60fps, using "hi-color" techniques where you change the color palette before each line is drawn. It was a ton of fun with a lot of problems like "aha, if I use this register for this value, it saves 2 extra cycles!".

My code's here: https://github.com/ekimekim/gb_music_video, and you can get a finished demo rom (which doesn't actually use any of the graphics stuff due to lack of assets) here: https://ekimekim.itch.io/steamed-hams-but-it-plays-on-a-game...

I should note that the technique I used for audio on the Gameboy was taken from this excellent video: http://tasvideos.org/5384S.html

8bitsrule• 8 years ago

While I'd rather listen to Costello with 16 bits at 24 kHz ... this is a very cool hack - thanks for sharing. Makes me (once again) sorry I gave away my 64!

A 48Khz digital music player for the Commodore 64

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