I have been trying to set up an instrument in which the filter's
cutoff-frequency  "tracks" the current note being played, similar to
keyboard tracking in commercial synthesizers.  When I program a passage 
which simulates legato, the filter clicks at the beginning of many of
the notes.  The problem is apparently coming from the filter because
when I remove the filter the legato is quite good.  The filter opcode I 
am using is "tonex", but I have had the same problem with butterlp.

In attempting to fix this I have played with the filter's "istor"
parameter and also introduced a small amount of portamento between
the pitches, but the results are still not very good.  I wondered
whether anyone has encountered this and if so if there is a good
solution for it.  Would be very grateful for help.

Thanks.

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