[HN Gopher] Commodore 64 and Raspberry Pi 4 = Synth6581
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Commodore 64 and Raspberry Pi 4 = Synth6581
Author : fangorn
Score : 76 points
Date : 2021-06-18 09:19 UTC (1 days ago)
(HTM) web link (www.raspberrypi.org)
(TXT) w3m dump (www.raspberrypi.org)
| _flux wrote:
| I've sometimes wondered if neural networks could be used for
| replicating the differences between different 6581 chips, by
| having a computer automatically interrogate the chip and the
| neural network.
|
| Optimally the end result would be a 6581 chip model (or possibly
| just some parts of the chip) with 2d input indicating what kind
| of chip to use today, possibly another input for temperature, and
| then driven by those existing 6581 emulators.
|
| It could potentially use insane amounts of compute power just to
| run it, if it uses the same approach as those researchers that
| did a speech synthesizer that produced one sample at a time from
| the network.. But it could also have very compelling results.
| EamonnMR wrote:
| Still waiting on a neural network sampler. I'm worried that by
| the time someone makes one all of the sweet artifacts will be
| ironed out though.
| wdfx wrote:
| See also the AY-3-8910 if you cannot find a SID
| https://en.m.wikipedia.org/wiki/General_Instrument_AY-3-8910
| wazoox wrote:
| Well the SID has a powerful resonating filter, this one has no
| filter at all. It's a bit like using a banjo instead of a Les
| Paul...
| mattowen_uk wrote:
| With this, and the dual-SID add-on boards for real Commodore 64s
| there are not enough original SID chips to go around. Already
| hawkers on eBay rip them out of working C64s and sell them
| separately at jacked-up prices, to people who have managed to buy
| C64 motherboards at a lower price because they are missing their
| SID chips, probably in fact the very same SID chip they are now
| paying over the odds for separately.
|
| There are a few pseudo-SID hardware projects[1,2,3] that can
| produce 'good enough' SID-like sounds, maybe the more honourable
| thing is to rework this project into something that uses those ?
|
| ---
|
| [1] https://www.c64-wiki.com/wiki/SwinSID
|
| [2] https://github.com/Sgw32/UltiSID/tree/hal_usid
|
| [3] https://www.retrocomp.cz/produkt?id=2
| ben_w wrote:
| Thanks for those links; I was about to ask if we could just
| make new SID chips, but the RetroComp link in particular
| appears to be the answer "yes".
| unwind wrote:
| The ARMSID is a software emulator, running on an ARM
| microcontroller. While it's plug-and-play with the real
| thing, I would not equate it with a "new SID chip".
|
| For some it's probably fine, for others it's just not the
| same.
| foft wrote:
| There are FPGA recreations too which are not software
| emulation. Not quite an ASIC but realistically as close it
| at gets at this volume.
|
| [1]https://www.fpgasid.de/
|
| [2]https://www.facebook.com/plugins/post.php?href=https%3A%
| 2F%2...
|
| I'm working on the latter one, Sidmax, so if there are any
| questions happy to answer.
| tssva wrote:
| Since a lot of the distinctive sound of a SID comes from
| the analog components which still need to be emulated in
| a FPGA solution does an FPGA solution really get closer
| to the sound of an actual SID than a quality software
| emulation?
| foft wrote:
| FPGA does not really offer advantages of accuracy, though
| it does offer advantages in time precision. This is
| important when putting it inside a C64. Of course a much
| faster CPU can also be used to handle real cycle accuracy
| in sync with the original clock.
|
| Part of the sid sound comes from the non-linearity due to
| approximation in its design. For example the state
| variable filters are very non-linear on the 6581. It even
| differs significantly from each individual chip to
| chip[1]. The best software models I'm aware of are in
| residfp[2] and jsidplay[3]. After some work in octave I
| found the filter model can be recreated without the large
| lookup tables used in this software.
|
| Of course getting the digital part correct is also
| important. There is a lot of documentation on this
| resulting from the decap [4].
|
| Some features like bitfade, multiple driven bits in the
| wave corruption etc do not translate well to FPGA. They
| can be approximated with timers and lookup tables.
|
| [1] Filter response chart:
| https://csdb.dk/forums/?roomid=14&topicid=105719
|
| [2] residfp: https://bel.fi/alankila/c64-sw/index-
| cpp.html
|
| [3] jsidplay2: https://haendel.ddns.net/~ken/
|
| [4] Sid internals: https://sourceforge.net/p/sidplay-
| residfp/wiki/SID%20interna...
| jchw wrote:
| Although I haven't gotten any obviously resurfaced SID chips
| (something that, for one reason or another, does happen often)
| the majority of SID chips I've gotten off of eBay (sample size
| <10 for what it's worth) have been junk; either not working at
| all, or only partly working.
|
| Still managed to get myself a working dual SID configuration
| with one 6581 and one 8580. But even _That_ is obviously not
| ideal, since you can't do cool stereo SID with that, at least
| if you want to it sound good. I thought maybe it would be OK,
| but a lot of tracks really need one or the other, the filters
| are usually pretty mucked up on one or the other. But you know,
| beggars can't be choosers. Maybe I could do a stereo setup with
| one SwinSID.
|
| Even though I didn't grow up with a C64 though, man, nothing
| really beats the real thing when it comes to SID. It's a shame
| it's so damn challenging to emulate.
| ddingus wrote:
| Some people in the Parallax Propeller community have been
| hard at work on a high quality emulation. First gen is
| SIDCOG, and a second one, running at some 400khz is in
| development.
| coldacid wrote:
| You're forgetting about FPGASID[1], which provides dual SID
| capability and high quality simulation of the original SID's
| analogue parts, not to mention can be toggled between the two
| different SID chip versions. It also supports paddles, like the
| real SID chips, but unlike SwinSID.
|
| [1] https://www.fpgasid.de/
| krylon wrote:
| I used to know a guy who collected C64s in 2009, and he was
| complaining _back then_ that buying them on eBay was an
| exercise in trial-and-error, for the exact same reason that the
| SID chip was missing so often. :(
| rasz wrote:
| pi has enough grunt to perfectly emulate 20 sid chips /slaps
| forehead
| rzzzt wrote:
| Alternatively, it could emulate the entire system. Do you see
| this as a flaw?
| bencollier49 wrote:
| Perfectly? The SID is semi-analogue isn't it?
| rasz wrote:
| What you probably meant is no two SIDs sound the same.
| Emulated SID will fit in perfectly :) cant claim it sounds
| wrong when they all sound wrong in some way ;p
| slim wrote:
| An emulated SID won't fit precisely because two emulated
| SIDs would sound the same :)
| rasz wrote:
| You can customize filter curves for all of your emulated
| SIDs.
| EamonnMR wrote:
| I would gladly shell out for a kit of this.
| [deleted]
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