4 ms·

These are all valid points - in fact I have my own (almost-but-not-quite-finished) semi-retrocomputing project too: a cross-platform MOD (the old Amiga music fo

by rob74 5y ago

These are all valid points - in fact I have my own (almost-but-not-quite-finished) semi-retrocomputing project too: a cross-platform MOD (the old Amiga music format) player written in Go (https://github.com/nieware/go-modplayer https://github.com/nieware/go-modplayer). Which may not be useful to a lot of people, but at least it was useful for me getting better at Go. That's not to say all of the things I do in my spare time are useful though - most of the time I end up playing games or browsing HN, so even less useful than reimplementing version management for an ancient OS.

windenntw 5y ago
I took a small look at your repo and noticed a possible issue: while Gravis Ultrasound did linear interpolation of samples [1], on Amiga all sample replay was strictly non-interpolated [2] ... essentially on each display scanline the hardware would check the period down-counter and load the next sample if zero was reached. cf: [1] http://www.gravisultrasound.com/files/documentation/GUSFAQ.txt http://www.gravisultrasound.com/files/documentation/GUSFAQ.t... [2] http://bax.comlab.uni-rostock.de/dl/Paula_SystemTheoretic.pdf http://bax.comlab.uni-rostock.de/dl/Paula_SystemTheoretic.pd...
- rob74 5y ago
  Thanks for looking at the repo and for the links! Initially I just used non-interpolated output, but it was extremely noisy. I suspected the Amiga had some additional analog hardware which avoided this, so I just added some interpolation to make it sound better. But anyway, it's far from finished, if I have the time to pick it up again someday I could make it more accurate...
  - windenntw 5y ago
    Yes, it has a low-pass-filter that you can turn on or off. See http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/node00EE.html http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_gui... and more generally: http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/node00E8.html http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_gui...

by rob74 5y ago

windenntw 5y ago

I took a small look at your repo and noticed a possible issue: while Gravis Ultrasound did linear interpolation of samples [1], on Amiga all sample replay was strictly non-interpolated [2] ... essentially on each display scanline the hardware would check the period down-counter and load the next sample if zero was reached. cf: [1] http://www.gravisultrasound.com/files/documentation/GUSFAQ.txt http://www.gravisultrasound.com/files/documentation/GUSFAQ.t... [2] http://bax.comlab.uni-rostock.de/dl/Paula_SystemTheoretic.pdf http://bax.comlab.uni-rostock.de/dl/Paula_SystemTheoretic.pd...

rob74 5y ago
Thanks for looking at the repo and for the links! Initially I just used non-interpolated output, but it was extremely noisy. I suspected the Amiga had some additional analog hardware which avoided this, so I just added some interpolation to make it sound better. But anyway, it's far from finished, if I have the time to pick it up again someday I could make it more accurate...
- windenntw 5y ago
  Yes, it has a low-pass-filter that you can turn on or off. See http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/node00EE.html http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_gui... and more generally: http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_guide/node00E8.html http://amigadev.elowar.com/read/ADCD_2.1/Hardware_Manual_gui...