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A new breakthrough! Just implemented a low-pass filter. Check out the attached .tap - first pattern is without the filter, second with low-pass enabled.

The low-pass is implemented with this simple algo:

y[i] = a(x[i] - y[i-1])

where y is the actual output volume level, x is the unfiltered output, and a is a (time-related) constant, in this case 0.25. Using a = 0.125 gives better results, but I'd need to implement more volume levels to use it.

I tried implementing a high-pass, too, but so far no luck on that, because the algo for that can produce negative values (unlike the low-pass one where the result will always be >=0). The high-pass algo I have is

y[i] = a(y[i-1] + x[i] - x[i-1]) 

Any idea how to modify it so it'll always produce positive results? I could probably invert the output but that'd be too slow I think.

EDIT: Nevermind, got it. The current implementation is ugly as hell, but hey, it works

Ok, so most of you have probably all seen this elsewhere already:

https://www.youtube.com/watch?v=FVGYi-46G2s
http://irrlichtproject.de/downloads/dmg5th.gb

Good old pulse interleaving on the 2nd DMG channel while resuming normal operation on the other channels. Been meaning to do this for a long time, and it was also clear early on that this would have to be some sort of an April Fool's prank - so thanks for inspiring me, garvalf

So, lessons learned? Well, 1-bit sound is possible on the Gameboy. But, as Shiru mentioned, the Gameboy CPU is... eh... not exactly great to work with if you want to do something out of the ordinary. Not only does it miss more than half the Z80 registers, but also a lot of useful opcodes aren't implemented, and the ones that are there are almost always slower than on a regular Z80. HRAM is a nice feature but doesn't make up for the drawbacks. So the possibilities for 1-bit  on Gameboy are very limited. One could probably pull off a third 1-bit channel with a lot of fiddeling and loop unrolling, but overall I have to conclude that this platform really isn't worth it as far as 1-bit music is concerned.

Hi mate,
Sorry, I don't know this particular program. Was it monophonic, or did it do multi-channel music?
In any case, there is some old PC Speaker stuff here: http://cd.textfiles.com/psl/pslmonthly2 … /mus_spkr/
Also, Will Harvey's Music Construction Set had the Entertainer as a demo tune, you can probably find that on some abandonware site.

Agreed, for some engines the IO contention adds some very pleasant overtones/harmonics to the sound.

Yeah, composite only is a downer, but I can kind of understand why. HDMI is not feasible for this kind of projects, because of the insane licensing fees (5000 USD per year + 1 USD per unit). VGA on the other hand is pretty much as outdated as composite, so they were probably thinking "why add another legacy port". But I agree, would have been nice-to-have.

Not using RCA for audio on the other hand is indeed a bad choice, didn't realize they use jack.

Whoops, that sold out quickly! Well, good for them. I think it's an excellent project at a very fair price, made by some very experienced people.

It's probably just akward wording/translation, quite sure they mean regular beeper tunes.

On the other hand, if one wanted to take the rules literally, then a tune made with fluidcore/wtfx/qaop/etc would do the trick, since those are technically digi-engines

Yes! So the day has finally come
Ummm... I don't have a Portfolio. Is there an emulator that can run this, and/or could you share a recording of the sound?

Well said, my friend. That's indeed one of the reasons I'm hooked on 1-bit music. There's a lot of uncharted territory waiting to be explored.

Perfect, this is exactly what I had hoped for. Thank you very much!

One little question, is it still possible to configure the color scheme? The current scheme isn't bad at all, but I like to work with a black background.