Preventing Misfires and Undesired Gates
When using the
PI
to generate gates from drum
machines with long decays or drums with lots of
resonance, you may experience “misfires”
,
or
undesired gates. This can usually be fixed by adjusting
the
PI
’s
Sensitivity
and
Sustain
knobs.
For this example, the input signal will be a techno track
that has a bass drum with about 150ms of decay. Our
goal is to have the
PI
generate a pulse whenever the
bass drum fires. In
Figure 10
, the green waveform on
top is the input signal, and the blue waveform on the
bottom is the
Gate
output of the
PI
. We see that three
gate pulses are generated when the drum fires, which
tells us the
Sensitivity
is set too high and the
Sustain
is set too low. The second pulse is being generated by
the decay of the input source which the
PI
mistakenly
interprets as a second "hit”. The third pulse is being
generated because the gain setting is so high that the
slightest change in voltage is interpreted as another
“hit” by the
PI
.
Setting the Correct Gain
In
Figure 11
we’ve reduced the gain by flipping the
L|
M|H
switch to L, removing one of the misfires. In order
to get rid of the second misfire, we need to adjust the
Sensitivity
or
Sustain
.
Adjusting Sensitivity
In
Figure 12
, we’ve turned the
Sensitivity
knob down
until only one pulse is generated. This technique works
best when using samplers, drum machines or any
source with repetitive sounds and consistent
amplitudes.
Adjusting Sustain
With input sources of variable or inconsistent
amplitude, such as an acoustic drum or a live
recording, turning
Sensitivity
down might result in
missed triggers (producing less pulses than desired). In
these situations, a better technique is to adjust
Sustain
.
When
Sustain
is turned up, the gate length will extend,
as seen in Figure 13. No additional gates will fire as
long as the gate is high. By setting
Sustain
high
enough that the gate is high for the entire bass drum
decay period, misfires will be prevented. The gate
length can be varied between 6ms and 560ms.
Properly adjusting
Sustain
reduces the likelihood that
changing
Sensitivity
will cause a misfire, allowing the
PI
to work better with live drums, mic sources and
sounds with long decays. Keep in mind that if
Sustain
is set too high, a rapid sequence of drum hits will miss
pulses, since the
PI
won’t re-trigger as long as the
Gate
is high.
An advanced technique for preventing misfires is
discussed in the next section.
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Figure 10
Figure 11
Figure 12
Figure 13
