Elektron Musical Instruments

those are good questions!  

The answer is, 

1) there are d/a converters inside the SID!  

	1) one for each envelope generater
	2) a 12-bit one for each voices waveform
	3) an 11-bit d/a for converting the digitl filter setting into
           an analog input to the filter control voltage. 

and 2) the filter is a standard State Variable Filter design.  There may or
may not be SVF chips out there, but there certainly are a thousand 
SVF schematics.  The design is basically three or four op-amp's, some
resistors and two capacitors (the two 2200pf polystyrenecaps you see on the
board next to the SID.  The op-amps are connected as two integrators
with negative feedback.  SVF circuits will still always differ from the SID's filter, 
however, because the SID analog portions are more like hybrid digital and
analog.  Specifically, the op-amp's are not linear.  This causes all kinds
of subtle coloring of the sound which will vary with the volume of a voice.

an excellent source of information on this stuff is the interview
with Bob Yannes:  http://stud1.tuwien.ac.at/~e9426444/sidpage.html  

hope this helps!

-N

On Wed, Apr 17, 2002 at 03:58:24PM -0400, Andrew Barthle wrote:
> ok, i know that the sid has analog filters in it. im curious as to how they
> work and if there are similar chips available as stand alone parts.
> basically, i want to know how one can filter analog audio, while being
> controlled by a digital circuit. i'm sending this message here since i
> expect that some of you have intimate knowledge of the sid and maybe even
> make your own equipment. thanks.
> 
> -- 
> Andrew Barthle
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> 
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> 
>  
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