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Forums > C64 Composing > 6581/8580
2020-06-27 00:59
rupy

Registered: Mar 2020
Posts: 8
6581/8580

Is there some good reason SID music is not released with both 6581/8580 versions? Most tunes are only released for 8580 and some sounds play to low on 6581. Is there some way to convert 8580 tracks to increase the volume of the sounds that are too low on the 6581?
2020-06-27 01:23
Jammer

Registered: Nov 2002
Posts: 916
Not quite possible to recreate exactly 8580 tune on 6581. Old sid is just too little punchy and suffocates quickly on more powerful sounds. 6581 bandpass filter is practically useless :/
2020-06-27 01:33
Mixer

Registered: Apr 2008
Posts: 328
Most 8580 sound equal to other 8580. Nearly all 6581 chips sound a bit different from other 6581 and 8580. Therefore the composers tend to do music for a specific SID chip, and since most 8580 sound the same, it makes sense to do music on them. Listeners can then all hear the intended sound.

Emulators allow changing the chip type and filter cut off, but the 8580 and 6581 will always sound a bit different.

Also, there are some combiwaveforms, which simply do not work on some chips and are therefore silent.

One could do some "on the fly" filter cutoff/resonanse or ADSR re-mappings on some buffered sid player, but they usually do not work well.
2020-06-27 10:50
OSC

Registered: Nov 2006
Posts: 721
Quote:
One could do some "on the fly" filter cutoff/resonanse or ADSR re-mappings on some buffered sid player, but they usually do not work well.

Indeed, this is only thing that can be done, but even so you still wouldn't get the deep bass effect as you would on 8580 for some SIDs. The same goes for 6581-only SID which can accomplish high quality cutoff when set at higher frequencies.

A filterless SID is the only way to accomplish 6581/8580 friendliness.
2020-06-27 12:38
Mibri

Registered: Feb 2018
Posts: 69
^
No filters, and no combined waveforms, yes. You'll have to prise my filters and combined waveforms from my cold, dead hands. So to answer the two questions: yes, and no. :)
2020-06-27 14:41
TheRyk

Registered: Mar 2009
Posts: 730
you can look for filter writes in memory of an idividual .SID file and fiddle around with written value in monitor until it sounds halfways ok on the desired hardware SID. I wouldn't know how to do that universally, however
2020-06-27 17:12
Mixer

Registered: Apr 2008
Posts: 328
@TheRyk: F.ex. disable i/O(d000-e000), have the player to write values to the ram under the I/O. Then modify values, enable I/O, and write those values to corresponding sid registers.
2020-06-27 20:10
rupy

Registered: Mar 2020
Posts: 8
So these filters, is there an example of what they do that I could download? So for example the same song with and without filters to get a more intuitive feeling for why they are so important!
2020-06-28 16:27
Frantic

Registered: Mar 2003
Posts: 1442
rupy: I didn't find a good demonstration right away specifically for the C64, but here is a video that demonstrates a basic filter (cutoff frequency and resonance) and even though the filter in the C64 doesn't sound exactly the same, the general principle is the same:

https://www.youtube.com/watch?v=8K8YnPqfxyk

The filter in this video is a low pass filter, which filters away high frequencies from a sound. The C64 also has high pass filter (filters away low frequences) and band pass filter (filters away frequencies outside of a certain range) and you can also combine the filter types at the same time.

In essence, the filters vastly increase the number of sounds that can be produced, even using the very same underlying waveform. That is why a C64 sounds so much cooler than a NES or so.
2020-06-29 03:14
Adam

Registered: Jul 2009
Posts: 264
Quote:
Is there some good reason SID music is not released with both 6581/8580 versions?

I try and make some songs compatible with both, sometimes I don't. I like to use both SIDs but I do prefer the 6581's filters and distortion. I think the sound of the 8580 is too sterile. The imperfections of the 6581 is what makes it sound great to me.
2020-07-01 21:39
acrouzet

Registered: May 2020
Posts: 4
The 8580 filter can achieve lower cutoff frequencies than the 6581, which can produce deeper, punchier sounds. Unfortunately, this means that a large number of 8580 tunes can't really be converted to 6581 without some sacrifice in sound.
Also, The filter cutoff frequency on the 6581 increases exponentially as you increase the cutoff value, but the 8580's cutoff increases linearly. This makes things even more complicated for conversion between the two chips. Perhaps one could make a lookup table for converting frequency values from one revision to the other?
2020-07-01 22:44
Frantic

Registered: Mar 2003
Posts: 1442
Yes, using different lookup tables would go some way to make the same tune sound more similar across the chips. Only problem is that there is also a lot of variation between different 6581 chips for example.

Some of the variation can be seen here:
2020-07-02 01:08
McMeatLoaf

Registered: Jan 2005
Posts: 92
The red, Follin-style curve isn't even at the end of the range, zerozillion had a chip with CF ~1000 Hz at register value $0. 6581 filter curves be crazy.
2020-07-02 02:00
acrouzet

Registered: May 2020
Posts: 4
Quote: Yes, using different lookup tables would go some way to make the same tune sound more similar across the chips. Only problem is that there is also a lot of variation between different 6581 chips for example.

Some of the variation can be seen here:


Yeah, that's true. I remember hearing that Martin Galway said the player for Terra Cresta originally had an option in which you could adjust the filter according to your own SID, but it was never implemented into the game. I wonder why nobody else has done that since then (to my knowledge).
2020-07-02 09:27
OSC

Registered: Nov 2006
Posts: 721
Quote:
Yeah, that's true. I remember hearing that Martin Galway said the player for Terra Cresta originally had an option in which you could adjust the filter according to your own SID, but it was never implemented into the game. I wonder why nobody else has done that since then (to my knowledge).


The menu screen of L.E.D Storm had this option from what I remember, whether it was documented in the manual or not.

L.E.D. Storm
2020-07-02 13:53
Groepaz

Registered: Dec 2001
Posts: 9358
Beach Head II too
2020-07-02 20:17
Rastah Bar

Registered: Oct 2012
Posts: 227
And the 1984 game "Havoc"
http://www.gb64.com/game.php?id=3436&d=18&h=0
2020-07-06 16:48
booker

Registered: Jul 2003
Posts: 325
Quote: Is there some good reason SID music is not released with both 6581/8580 versions? Most tunes are only released for 8580 and some sounds play to low on 6581. Is there some way to convert 8580 tracks to increase the volume of the sounds that are too low on the 6581?

I guess there are these cards which take both SIDs and you get it to play the tune on both the same time. Just choose the output. Solved.
2020-07-30 11:59
rupy

Registered: Mar 2020
Posts: 8
Would it make sense to have two official csdb 6581/8580 categories or tags? So one can filter and search on them?
2020-07-30 16:03
booker

Registered: Jul 2003
Posts: 325
Quote: Would it make sense to have two official csdb 6581/8580 categories or tags? So one can filter and search on them?

maybe no need for tags, since tunes got that in PSID info.
2020-07-30 16:11
rupy

Registered: Mar 2020
Posts: 8
Aha, so csdb could automatically fetch that from hvsc and display it?

Edit: I just realized it is displayed on the sid page, but not the release even if it is a music release.
2020-07-30 16:18
iAN CooG

Registered: May 2002
Posts: 2729
https://hvsc.de/
advanced search for sidmodel. Be aware that not all tunes have a known intended sidmodel set.
2020-07-30 18:11
TheRyk

Registered: Mar 2009
Posts: 730
Quoting acrouzet
I wonder why nobody else has done that since then (to my knowledge).

In addition to the ones already mentioned by others, I recall the game Madness /Rainbow Arts/Chris Huelsbeck had filter adjustment.

Also in Delta/Thalamus/Rob Hubbard (Title Tune only) the last options "FX" might refer to filter value, not sure though, might also just add an option resulting in totally different tune ^^
http://hvsc.perff.dk/MUSICIANS/H/Hubbard_Rob/Delta_Mix-E-Load_l..

And yes, it _was_ indeed rare :)
2020-07-30 23:18
F7sus4

Registered: Apr 2013
Posts: 17
@TheRyk: My main concern is that even though the user had the possibility to adjust the filter, it was still his subjective choice that didn't necessarily reflect composer's concept. (If it would be possible to examine filter curve of each particular SID6581 and automatically re-adjust it via cutoff offset to the expected sound, that would mean a lot.)
2020-07-30 23:40
Groepaz

Registered: Dec 2001
Posts: 9358
Then again, when you like what you hear, how does the composers concept matter?
2020-07-31 06:21
Grue

Registered: Dec 2001
Posts: 136
Slightly off-topic, but if you are unfortunate to own 6581 that is too dark (filters too much) you can try to compensate it by changing filter caps to lower value, like 470pF to 330pF, or even to 270pF. Be sure to use high quality matched pairs for best results. Commodore didn't care much about the high-quality part so filter nonlinearities are part of the wrong kind of filter caps used by Commodore, ceramic vs plastic film ones.

And for the topic, game Raid over Moscow also includes filter compensation menu :)
2020-07-31 22:00
TheRyk

Registered: Mar 2009
Posts: 730
@OT yeah the board environment can have a great impact, but do we really want to go there in this fred? :)
2020-08-01 01:27
McMeatLoaf

Registered: Jan 2005
Posts: 92
If you want to find a fitting filter curve on a per-composer or per-tune basis, you could SIDdump the entire tune(s) (assuming that the same 6581 was used in all tunes), listing and sorting all the cutoff register values on a per-frame basis, mapping these (cutoff value->filter curve->cutoff freq) then picking the filter curve with the largest standard deviation of log(cutoff freq).

Or you could list the highest note filtered with a certain cutoff value (say freq $1000 at cutoff value $10), picking a filter curve where the cutoff freq at that register value doesn't go below that note (or 0.5x the note frequency or whatever).

Note that neither of these tricks work very well for David Dunn's tunes.
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