MOTM

The filters are different topologies, which pretty much dispels the myth
that the "CS80 custom chips are integrated versions of the discrete
circuits in the GX1."  Both exhibit some basic similarities (the 480 is a
pair of 2nd-order filters, each 485 is a single 2nd-order filter), both
have specific feedback-damping to prevent self-oscillation, although I
increased the adjustment on the 485 to let it introduce "bad" IM
distortion, because it sounded musically useful.  The bottom line is, they
sound different.

  Yamaha must have had this great fear that a keyboard player would be
able to place a filter in a state that made it appear as if the instrument
was broken; things like closing the high-pass filter all the way such that
no tone was heard.  Thus, Yamaha built the GX1 HP-VCF to respond to 1/2
Oct/V modulation wheres the LPF was 1V/Oct.  Similarly, the CS80 HP filter
is hardwired to track and half the distance as the LP filter on its
modulation input.  On the MOTM-480, this hardwired behavior is part of the
FM input (1V/Oct still tracks the same for both filters, same as in a real
CS-80).

  Hope this helps(?)

Crow
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On Mon, 23 Aug 2004, tontaub wrote:

> That said how does a single 480 compare to a pair of 485s?
> 
>    :-) Michael.