3D Model
The idea for this project came when
Ken was listening to some music in which part
of the background was jumping between octaves
in a semi-random fashion. Feeding noise into a
comparator was my immediate thought, but he
soon realized this wasn't going achieve what
he wanted. Ken needed to be able to control
when these jumps could occur. As such, some
form of memory element was required, into
which the level could be clocked when
required.
Ken has used an 8 stage digital shift
register as the memory element. Each clock
pulse, the remembered level (logic 0 or logic
1) is moved into the next stage "bucket
brigade" fashion, and the new value stored in
the first memory cell. The result is a random
level (on or off) at a predetermined time at
the first output, plus time delayed versions
of previous levels across the remaining
outputs.
As well as the 8 shifted gate outputs
available, the raw comparator output is also
available. The status of each of the outputs
is displayed by a LED, making adjusting the
unit so much easier.
There is also a secondary voltage
control input so the comparator
break/reference point can be varied by an
external control voltage. On top of all this, there is a D/A
converted connected to the outputs of the
shift register, with the last 4 bits capable
of being switched in or out. This gives some
great little melodies or sequences. They will
depend largely on what is fed into the shift
register, though due to the configuration will
always have a certain flavor.
There is an inverted output for this
as well. When the resultant voltage is fed to
a VCO, effects from subtle semi-random
melodies to 70s sci-fi computer sounds can be
generated.
The later version adds a 'LOOP' input
so that several gated comparators can be
cascaded together, or its own output can be
fed back into its input. Other digital sources
could also be used. This new "digital" input
is OR gated with the original "analog" input,
so keep this in mind when patching. It is
quite possible to rapidly set all stages in a
loop to HIGH, in which case there will be no
further activity on the outputs.
The BoCGS SWAMP uses the Gated
Comparator and incorporates a Klee-type
sequencer using the CGS304 DC Mixer.
CGS13
Tutorial By Nicholas
Peck At 'Under The Big Tree'
