1. First steps in Reaktor Core - Native Instruments

6.28319 is 2*π, which is then divided by the sampling rate, forming the value
to be multiplied with the cutoff frequency. We don’t need a modulation multiplier,
because F logically is a control signal input, so we might perform the
initial multiplication even if there is no initialization event at the F input.
We perform the division before the multiplication, because the division
is relatively heavy on the CPU, and the sampling rate doesn’t change
that often. If only the cutoff frequency changes, there are no events
sent to the divisor module, and therefore, the division will not be performed.
This is one of the standard optimizations that can be done by
the core-structure designer.
Let’s build the circuitry implementing the filter’s equation:
The audio input is latched just in case events at this input arrive asynchronously
to the standard audio clock. That wouldn’t be necessary in the core-cell
structure, where an audio input is known to send events at correct times, but
in a general core macro it is a very good practice.
Two modulation multipliers are used to prevent events at the F input (which
generally speaking, can happen at any time) from triggering the computation
in the feedback loop. Here it should be more clear why they are called
modulation macros, in this case the cutoff-derived signal is used to modulate
gains in the feedback path.
Latching is a standard Reaktor Core technique to make sure that incoming
events do not trigger the computations at improper times. It’s also
very widely employed in the form of modulation macros and in other
similar situations.
The Z^-1 module is used to store the previous output value and will automatically
send an event with the previous output value on every audio clock tick.
It also takes care of possible denormal values which otherwise could occur.
Those familiar with DSP should notice that the structure looks pretty much
similar to the standard DSP filter diagrams.
The Merge module at the adder output is making sure that the filter state
REAKTOR CORE – 103