28 Mar
2006
28 Mar
'06
7:24 a.m.
On Mon, 27 Mar 2006, Jim Battle wrote:
The chip is a hybrid digital/analog chip. Duplicating
it via pure
digital means would be hard. Apparently too the chip had bugs and so
are unspecified, but people exploited those bugs for generating sound
effects.
The hybrid nature comes more from using digital components for analog
purposes. A "proper" state-variable filter is made with opamps or a
Moog-style transistor ladder. The SID's filters are made with digital
inverters and that's where a lot of the unique flavor comes from. Because
the PhoenixSID's filter is made of discrete CMOS inverters, I'm guessing
that pulling such a stunt in FPGA is difficult.
--
David Griffith
dgriffi at cs.csubak.edu