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Repose
Registered: Oct 2010
Posts: 225 |
Ultimate reverse engineering
This person took 32 chips of every revision, connected them to a custom clock source and ran them independently, to read out the OSC3/ENV3 of every combination, plus analog recordings. He wrote an emulator which recreates every register setting and measures all the variations within and between chips. Its an amazing amount of work. He also reverse engineered CIA's as well, as those are needed for "real sid" type tunes, which require emulating the entire machine for music playback.
https://www.youtube.com/watch?v=pePq68HaI7M
Emulating the SID the HARD way.
plgDavid
Here is one of the "torture test" tunes which require very accurate emulation of a specific model, it sounds amazing:
https://www.youtube.com/watch?v=BVevORuyQ_8
Jammer - Club Stylier
Club Stylier
Forever 2010 - #1 |
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spider-j
Registered: Oct 2004
Posts: 498 |
Also: what are "real chips" in the 6581 realm anyway? I feel 6581 will be lost in translation because everybody had a different one and even remembers it differently. There's a reason everyone uses 8580 nowadays.
When I read threads like this I'm quite happy that I got my first C64 so "late" and it's normal for me to listen to 6581 tunes on 8580.
Bought me a couple of 6581s in ~200X – afair they all sounded different. Regardless of "revision". |
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
Indeed a LOT of this "doesn't sound like a real chip" can be attributed to "doesn't sound like i remember it from my c64". Which is exactly why many ppl will not be able to tell what is what in a proper blind test (containing various recordings from emulators and different chips).
Reminds me how years ago i uploaded two recordings, both from reSID and only different in volume, and people were convinced one of them CLEARLY is the broken emulator :) |
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Frantic
Registered: Mar 2003
Posts: 1648 |
Quote: There's some stuff emulated here that isn't in ReSID, such as oscillator leakage and the variation in combined waveforms between chips. Apparently the elusive R1 is emulated too. ReSID's 6581 filter also has a few bugs, so I'm wondering if this emulation is an improvement overall.
What's "oscillator leakage"? |
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acrouzet
Registered: May 2020
Posts: 97 |
Quote: What's "oscillator leakage"?
An oscillator's volume level being 0 still lets some of the oscillator's signal through. You can hear this in many demo recordings on YouTube. When a tune has faded out, you can still hear the SID voices very faintly holding the last sound register values. |
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acrouzet
Registered: May 2020
Posts: 97 |
Quote: Also: what are "real chips" in the 6581 realm anyway? I feel 6581 will be lost in translation because everybody had a different one and even remembers it differently. There's a reason everyone uses 8580 nowadays.
When I read threads like this I'm quite happy that I got my first C64 so "late" and it's normal for me to listen to 6581 tunes on 8580.
Bought me a couple of 6581s in ~200X – afair they all sounded different. Regardless of "revision".
6581 has some analog artifacts that emulators still don't get exactly right. They vary quite a bit between chips, but sometimes an emulator will do something that is rarely heard on a real chip, if at all. |
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F7sus4
Registered: Apr 2013
Posts: 117 |
Quoting acrouzetAn oscillator's volume level being 0 still lets some of the oscillator's signal through. You can hear this in many demo recordings on YouTube. When a tune has faded out, you can still hear the SID voices very faintly holding the last sound register values.
This is true. By the way, it is still possible to modulate sound with registers in that state and the result will lead to a lot of glitch-like interferences otherwise impossible to achieve. From what I see, this behavior is still yet to be researched (and possibly utilized) or at least I didn't find anyone else doing it to a larger extent before.
Quoting GroepazIndeed a LOT of this "doesn't sound like a real chip" can be attributed to "doesn't sound like i remember it from my c64". Which is exactly why many ppl will not be able to tell what is what in a proper blind test (containing various recordings from emulators and different chips).
It really depends on individual sensory receptivity and ear-training. No matter how precise the emulation will attempt to be, reSID will still remain distinguishable from the real chip in many circumstances, especially because of how organic the SID's lowpass filters sound at lower filter values. (Not mentioning SwinSID and its hardware alikes as they fall into the more obvious "I'm not a real SID sound" category.) |
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chatGPZ
Registered: Dec 2001
Posts: 11386 |
Quote:the variation in combined waveforms between chips.
This btw is - just like variations in the filters - something that is simply different, everywhere, and can not be attributed to some chip revision (for example). The difference between reSID and this new emulation (and also reSID-fp) regarding those thing is that reSID does not try to sound like a specific (real) chip. It sounds like "a" SID chip though :)
But yes, the emulators (also this new one, btw) do not simulate certain analog effects related to the mixed waveforms, but instead use tables for them. It will still take a while until this can be synthesized in real time (on a random pc anyway) :) |
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acrouzet
Registered: May 2020
Posts: 97 |
Quote: There's a demo of it here you can download and run:
https://www.plogue.com/downloads.html
(10 min per session and you can't save, otherwise it seems to be the same as the full version)
The emulated filter IMHO sounds quite different from reSID-fp or Sidplay3 and clearly closer to real chips. Too bad a few of the emulated chips seem to glitch on some David Dunn tunes, e.g. Elite (both subtunes).
If you're referring to the octave drops, its actually a thing some real 6581s do, its just rare. Like you said, only a few out of the many 6581s in the emulator do this. |
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Jammer
Registered: Nov 2002
Posts: 1335 |
'Club Stylier' is one of my old 'dead end' techniques back when I handled multi sounds with Attack set to 2 which is not the best and most stable thing to do with ADSR at such speed rates. Surely not doing it anymore ;)
Here's the leakage, btw:
https://youtu.be/YGxAWQzTzVo?t=75
Played with dual 8580 so glitch manifests on each chip separately with different delay (thus you can hear that left/right thing). Cutting sound with testbit or zero wave is the easiest way to reproduce. |
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