Erica Synths EDU DIY Dual VCA Eurorack Module Kit - Manual (Page 7)

more potential to be used and converted into flow. On the flip-side, if we make the
bottom narrowing tighter than the other, flow will de- and pressure in the middle will
increase.
An important thing to keep in mind is that when we’re just focusing on the pressure levels,
the absolute quantity of flow does not matter at all . It really is only about relations and
proportions. So regardless of wether we have a total flow of 5 ml or 5 l – as long as this is
half of what could potentially flow with just one narrowing, we e
ff ectively halve the applied
pressure.
Okay, but so far we’ve assumed the pressure at the top to be constant. An audio signal,
as we said earlier, is a swinging voltage though, meaning that it changes over time. In our
analogy, this would mean that our pressure is getting more or less intense – and
sometimes even going negative, essentially turning into suction. Now obviously, a voltage
divider works with audio signals. So it can handle big, small, negative voltages just fine,
always dividing them by the same factor. But why is that?
Because resistors have two
properties that make this possible: linearity and symmetry . Linearity, in this context,
means that there is a linear relation between the voltage applied to a resistor and the
current that’ll flow through it. So a doubling in voltage will always result in a doubling in
current.
Same thing applies for our analogy: if we double the
pressure, we get double the amount of water flowing
through our narrowings. Since this is true not only for
multiple narrowings in series, but also for each
individual one in isolation, our potential/actual flow-
model still works out the same way. Let’s look at this in
detail. For a doubling in pressure, we’d get a total flow
of 10 ml instead of just 5. Add a bypass, though, and
we’d see a whopping 20 ml flow through this narrowing.
Since 10 ml total is still half of these 20 ml that could
potentially flow, we (again) get half the applied
pressure between our two narrowings
.
Cool, but what about negative voltages? This is where
the second property – symmetry – comes in handy. For
resistors (and for our narrowings), the direction of flow
does not matter. The restrictive e
ff ect will be the same
in either direction. So if the pressure up top goes
negative, we simply add a minus sign before all our
values, indicating that the direction of flow has been
inverted.
But since -5 ml is still half of -10 ml,
everything still works out the same, and we get half
the pressure in the middle
.
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