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

Registered: Mar 2020
Posts: 6
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?
 
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2020-06-28 16:27
Frantic

Registered: Mar 2003
Posts: 1437
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: 262
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: 1437
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: 91
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: 720
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: 9327
Beach Head II too
2020-07-02 20:17
Rastah Bar

Registered: Oct 2012
Posts: 226
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: 312
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.
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