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Forums > CSDb Discussions > The 6581 has fallen into oblivion
2022-07-17 14:14

Registered: Apr 2004
Posts: 40
The 6581 has fallen into oblivion

Musicians seem to have lost interest for the original 6581 model.

Is it because of how it sounds (low resonant filter, combined waveforms) or because of technical challenges (huge filter variability between revisions, quality of filter emulation) ?
There are so many 6581 tunes that we all enjoy that I cannot believe the "sound" is the issue.
The funky distorted 6581 filter is absolutely loveable, not better or worse than 8580's, just different.

There are so many awesome examples..
Miami Vice
4-Mat's Filter
Dirty Pair

Now that reSID is doing a good job at emulating the 6581, I assume one of last issues is that musicians have no guarantee that a tune will be played back correctly, with the same filter characteristics that they used when composing their tunes. Especially when they're played on a real c64, it just cannot work perfectly.
As of today, even if we wanted to organize a 6581 music competition it would be laborious to play them back correctly even with an emulator.
Some extra info could be certainly added to a .sid header, but running the .prg in Vice would be more difficult, the SID player init code would have to write to some unused SID addresses to "configure" the SID. This would please all emulators but would have no effect on the real thing (except if it had an emulated chip)..

Do you believe the 6581 is doomed ? :(
... 32 posts hidden. Click here to view all posts....
2022-07-21 09:18

Registered: Nov 2021
Posts: 10
Quoting TheRyk
a) DON'T use filters at all (you'd be surprised how many cool tunes from the 1980s don't)

A favourite of mine is Orion by Jason Page. :)
2022-07-21 09:25

Registered: Nov 2021
Posts: 10
Also Morpheus by Steve Turner.
2022-07-25 01:36

Registered: May 2020
Posts: 23
Quote: Hi Conrad! ;)

Filtertype switching on 6581, as far as I remember.... There are ways of avoiding the clicking somewhat... Having 2 types active and only switching one of those off.... etc. I wonder if it also works with filtervoice control?

I believe what causes clicking when changing the filtered channels is changing the actual number of channels the filter is active on, so as long as you keep the amount of filtered channels the same at all times you shouldn't get any clicking.
2022-07-25 10:58

Registered: Nov 2002
Posts: 1202
In general, most clicking seems to be caused by enabling/disabling bandpass - also on 8580 ;)
2022-07-25 12:11

Registered: Apr 2013
Posts: 82
Quote: In general, most clicking seems to be caused by enabling/disabling bandpass - also on 8580 ;)

This is true for 8580, but on 6581 turning the filter mask on/off is just enough to trigger the clicking noise, no matter what the filter type is.

I didn't test acrouzet's approach yet, though I have a bit of doubt - even if it consistently worked that way, it would require an extraordinary amount of resources to become wasted only to keep proper filter ratios at all times. In the end, I think it's just easier/better to "hide" the artifacts among other sounds.

Quoting spider-j
I doubt it is even possible to convert any 8580 drum sound with fast filter switchting to 6581 without loosing the characteristics that defined the sound in the first place. You can adjust the values, but you can't reliably get rid of that horrible "pop" / "crack" sound when switching filter bands

Ed did a lot of great work when it comes to progressive 6581 sound (and especially drums).
2022-07-27 13:14

Registered: Oct 2006
Posts: 150
@Laurent: Jakob's Lullaby was made for 8580. The SID version in the file is wrong. I think the same goes for all the tunes in Another Beginning

Our latest demo Lifecycle was made for 6581, the grittier, the better ;-)
2022-07-30 17:18

Registered: Nov 2002
Posts: 47
following this post i thought i would make some experiments with goattracker. what i noticed first is that the click has more amplitude the more channels (+ext as fourth channel) you feed thru the filter.

as most of my songs are more sound experinments than composition i decided to dig more into "6581 filter pop drones".

looping a simple lowpass on/off table you can create a boring buzz, but if you switch to multispeed (4x) it is possible to create proper audible frequencies.

i thought then i would use these buzz drones to create a song.

i used the G#2 note and 432Hz tuning, because i fancy it and it created less vibration than using 440Hz.

I played some pwm sounds on channel 1, also with a looped pwm table, to have some interference sound counterpoint to the filterclick drone buzz.

further experimenting with the duty cycle of the filter on/off relation it was possible to create 4 different nicely audible octaves of this buzz.

the highest possible frequency would be generated by:
00 90FF
01 80FF
02 FF00

then i started to play with duty cycles, this generates the lowest possible audible frequency:
00 90FF
01 0200
02 80FF
03 0200
04 FF00

from there you can change lines 01 and 03 to 01/01, 00/01, 00/01 etc etc. all of them create either raspy sounding drones or a very phased sound.

but also inserting the small break after the switch will sound different than a 50/50 duty cycle.

and not to mention, one could even set different cutoff values during the on phase and further mangle the sound.

this all was very exciting and i started to evaluate which musical note would result in a neat sound in combination with the filter pop drone. sure this is very minimal, one frequency only (unless someone writes a routine to modulate framerate?) and the resulting sound is more atari than commodore, but that does not hurt me. the great thing is that it is very loud, and loud also does not hurt me much.

but then i encountered a problem, else i would have already written a full tune with this technique and called out for a compo:

my filter duty cycle modulation tables do not work! they only work when i use the table starting from 00. if i copy the values to 05 and call it from the filtertable pos the drone does not work. keeping the values in table pos 00-04 and editing them on the fly produces audible results always.

and on the other hand, probably it will sound totally off on the real thing (hello filter variations... what will it sound like at all). sure it will produce audible results, but the timbre would be very varied.

if anyone could help me finding out why it behaves like that and how these modulations would work from any position in the filtertable? this really could be something for a competition and yet another way to exploit the 6581, and to pull it out of "oblivion".
2022-07-31 01:05

Registered: May 2020
Posts: 23
4-Mat was able to create a pseudo 4th channel by modulating the filter-type and filtered channels settings very quickly, seen here in oscilloscope view: https://youtu.be/WKvJ3XkIz2Y

Keep in mind this is on 8580, so the clicking is much quieter here and is able to be mixed with the 3 SID voices better.
2022-07-31 09:50

Registered: Apr 2013
Posts: 82
Quoting acrouzer
4-Mat was able to create a pseudo 4th channel by modulating the filter-type and filtered channels settings very quickly, seen here in oscilloscope view

This particular trick was earlier used in the concluding part of Triangle My Amelie in the very same compo, but what is important is that it does not require the SID model to specifically be 6581.
2022-08-01 20:00

Registered: Apr 2004
Posts: 40
@Stone : Thanks for the info, who would have guessed !
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