Truth Tables
Boolean logic gates can be visualized with truth tables. These tables usually take two
inputs and compute one output. With Binary, there are six possible inputs, but the
fundamental principle remains the same.
The OR Gate remains low (0) when all inputs are low, and goes high (1) when at least
one input is high. The NOR Gate remains high when all inputs are low, and goes low
when at least one input is high. In the truth tables above, 0 represents 0V and 1
represents +5V.
S-Trig and V-Trig Conversion
The gate/trigger inputs on most synths, drum machines, and sequencers are activated
by a rising voltage (such as 0>5V). This is commonly called a V-Trig circuit. But some
devices use a different circuit called an S-Trig (or shorting trigger), in which the circuit
rests at a positive voltage and responds when the voltage drops to 0V.
Converting between these two standards is not as simple as inverting the voltage.
Passing a 0>5V gate signal through an inverter circuit will result in a voltage that jumps
from 0V to -5V when active. Since most gate inputs expect a 0>5V pulse, an inverted
gate is not generally usable as a logic signal. A positive offset is still needed to create
a pulse that activates the logic circuits used by most modular synths.
Binary is designed for logic signals in the positive (0V>5V) range only, so it can be used
for conversion of S-Trig signals to V-Trig and vice-versa, without the need for the
additional offset. This applies to drum machines and sequencers as well as “note on/
off” events generated by (or required by) some analog synths.
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