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

Registered: Mar 2020
Posts: 8

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

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

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

Registered: Nov 2006
Posts: 721
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

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

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

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

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

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:


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

Registered: Jul 2009
Posts: 264
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

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?
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