Whatever you do you should ensure that the gate signal that drives any
particular envelope does not arrive before the new pitch CV is presented
to the VCO. The stock Polysix exhibits an annoying trait in that the
first three voices are actually triggered before the pitch CV is updated
to the new note. Hence, with patches that use a fast attack, the first
three voices click slightly if the difference between the previous note
played on that voice is significantly different in pitch to the new note.
The difference in time varies per voice but voice two has the worst
delay with gate being applied 2mS ∗before∗ the CV. Voices 4, 5 and 6
have their gates applied a good 2mS ∗after∗ the CV is updated so do not
click. 2mS might not sound that much but it's enough to produce an
audible click particularly if the patch is one with low harmonics.
I had thought this was an offset error or bleedthrough problem within
the voice VCA. But the randomness of the clicking led me to look
elsewhere. All the polysix units I have seen exhibit this problem and,
indeed, it's even audible on the many Youtube demos.
A quick way to test this is play is choose a patch with a fast attack
and fast release, no EG sweep to the filter and set the filter to a
dullish sound. Press the top C note six times to load the highest note
into each voice. Then press the lowest note on the keyboard six times.
You should hear three of the voices produce a noticeable click while
three of them don't. Continuing to press the same note again will not
produce the same clicking because now the voices don't have to change
pitch. If you can hear an appreciable click still you need to adjust the
VCF offset but that is a different problem.
If one is designing the key assigner from scratch one should able to
avoid this problem by writing the pitch information before any new gates
are sent out from the latches.
If you have a stock Polysix you can do what I have done and that is
build a triple gang gate delay circuit from a handful of components.
This delays the gate signal for around 3mS and completely silences the
pre-note glitching. I'll pop up a schematic at some point if any one is
interested in doing it themselves.
Tony
http://takla-makan.bandcamp.com/http://www.oakleysound.com