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  • Joined: 01 Jan 2014
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SN76489, Beyond 50/60hz
Post Posted: Sun Feb 12, 2017 12:13 pm
Hi,

Many interesting things have been happening with the SN76489 of late. Sneventracker was recently released and has expanded interest in the chip. TMM12 released a 392hz chiptune for the Battle of the Bits Winter Chip XII competition and there was some discussion about the legitimacy of the tune.

http://battleofthebits.org/arena/Entry/SMStep/24092/

Calindro and I hacked together a rom to demonstrate the tune playing on hardware. It is a quick hack job and as such not perfect but good enough to give demonstration. It requires PAL (sorry) and i strongly recommend Emulicious or real hardware.

It is interesting to consider possibilities past 50/60hz. Samples, amplitude modulation, FM being thrown in to the mix as compliment for PSG, etc. Anyways if you are interested in SMS Music now is a good time to hit Battle of the Bits, Soundcloud and youtube and check out what is happening with PSG.

Thanks to Tmm12 for permission to use tune, thanks to sverx for psglib which we used in rom and thank you to Hertzdevil for making Sneventracker.

Oh and shameless plug... If you are new to the site there is an SMS Power Comp late March which includes music category. Entries can be PSG, FM or wild. Wild entries need to be remix of existing SMS game music. Check out the Competition sub forum closer to the date.

Psidum / Calindro.

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  • Joined: 05 Sep 2013
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Post Posted: Sun Feb 12, 2017 4:45 pm
Even if I never tried using PSGlib at higher frequencies, I remember once somewhere on this forum we were discussing about calling PSGFrame function more than once per (video) frame, and that would make higher 'resolution' VGM playback possible. Probably slightly more complicated to do that in an actual game... but still possible, why not? :)

edit: AFAIR DefleMask supports whatever frequency too.
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  • Joined: 31 Oct 2007
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Post Posted: Sun Feb 12, 2017 5:57 pm
You can run your sound engine via line interrupts, just the question becomes how much CPU time are you gonna use up on music. The denser timing the more power is going away from the game or whatever, but if music is made for the sake of music you can spend all the CPU time on it, and can get very interesting results.
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  • Joined: 30 Jun 2016
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Post Posted: Mon Feb 13, 2017 12:49 am
For anyone curious what the track looks like.
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Post Posted: Mon Feb 13, 2017 9:52 am
@Psidum/Calindro: to make the ROM, did you split the tune into smaller parts or are you using uncompressed PSGs and bank switching into slot 1 and slot 2 "shifting" the tune over them?
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Post Posted: Tue Feb 14, 2017 2:05 am
@sverx: Both. Compressed in to smaller segments then linked together via watching for previous segment to end. Banks are switched before playing next segment. I can send you the code if you want but its what you would imagine, hack job polling vcounter for timing, undocumented ugly code. Most of the work was prepping the vgm.

Hitting the PSG faster than vblank isn't new but this was the first chiptune for the SMS i have seen doing it, might be others not sure. It would be cool to see more of this stuff.
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Post Posted: Tue Feb 14, 2017 6:46 am
There were some experiments before but no real chiptunes. There have been some using an underclocked PSG.
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Post Posted: Tue Feb 14, 2017 8:58 am
psidum wrote
I can send you the code if you want but its what you would imagine, hack job polling vcounter for timing, undocumented ugly code


No, please, have mercy ;) :D LOL
BTW I wonder what's the size of the original VGM... 2' 52" at 392 Hz... your ROM is 128KB and it's using compressed PSG...
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Post Posted: Wed Feb 15, 2017 1:43 am
The original VGM was 396,679 bytes uncompressed.
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  • Joined: 08 Apr 2008
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Post Posted: Fri Feb 17, 2017 3:37 pm
Have any of you checked out Aly James's Super PSG program? He released this VST some time ago, which allows you make songs and demos from the SN76489 using MIDI controllers, even letting you manipulate the chip in a way to generate AY chip-like envelope effects, create artificial waveforms from the volume registers, change the LFSR algorithm, or do PCM effects, just to name a few, and using the right tools to make them into VGMs.

Frankly, I haven't made any tunes from this since I'm not really proficient in using MIDI controllers and working with VSTs to convert them into VGMs, but this looks promising IMO.

You can find the plugin here:
http://www.alyjameslab.com/alyjameslabsuperpsg.html
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Post Posted: Fri Feb 17, 2017 10:24 pm
Yeah i have seen it. Not all of it is compatible with a real SN76489 but a large portion is. Pretty cool stuff.

He wrote proof of concept ROM for amplitude modulation for megadrive / genesis, the technique is equally viable master system.

https://soundcloud.com/alyjameslab/psg-only-timer-fx-mod-test-spsg-vst-link-to-v...
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