10.6

249Logic Pro Effects
Phat FX filter types: comb filters
A comb filter mixes the original signal with one or more copies of the signal, which are
delayed by a very short time interval. At some frequencies this mixture causes phase
cancelations, while at other frequencies it causes reinforcements. The result is a spiky
frequency spectrum with multiple resonant peaks. Graphically, these peaks resemble
the teeth of a comb, which gives this filter type its name.
Phat FX offers three comb filter designs, each with its own character. The best choice
depends on your preference and the type of sound you are trying to create. That said,
there are some distinguishing characteristics that may help guide you.
Comb Pos uses positive feedback on the delay lines, while Comb Neg uses negative
feedback to produce less extreme effects, often with a hollow quality. These two are
the less powerful combs and offer a much more gradual increase in resonance. They
can be useful when you require either a less dramatic effect or you want to hear more
of the exciter signal character in your sound. The latter point is noteworthy as this trait
can be useful when you want a more naturalistic sound.
Comb PM uses bipolar feedback on the delay lines. The resonance control is bipolar,
allowing you to freely shift from negative (hollow sound) on the left to positive (bright
and peaky) on the right. This comb is useful for classic bright Karplus-Strong style sounds,
where the exciter impulse is not easily heard and the comb is more prominent. Take care
with your resonance level because it is capable of quickly going to extremes, which can
lead to feedback. Start with a resonance level of zero and increase (or decrease) slowly
to find a suitable effect strength.
• Cutoff: Controls the delay time in the comb circuit. Lower cutoff values equate to a
longer delay.
• F-Back: Controls the amount of feedback in the comb circuit.
• Damp: Softens the frequency peaks in the comb-filtered spectrum.
Note: Sending a percussive sound into a highly resonant comb filter causes it to
ring at a frequency determined by the delay time you have set with the Cutoff knob.
Phat FX filter types: ring modulation
Ring modulation is a process in which a modulator and a carrier signal are multiplied. Each
frequency component of the modulator interacts with each frequency component of the
carrier to produce two sidebands: a sum and a difference (carrier – modulator). When a
filter is set to the RingMod type, the signal entering the filter acts as the modulator, while
the carrier is supplied internally by the filter.
• Frequency: Controls the carrier frequency.
• Mix: Applies a constant offset to the carrier.
• At 0%, the carrier wave varies between –1 and +1, resulting in classic ring modulation.
• At 100%, the carrier wave varies between 0 and 1, resulting in classic amplitude
modulation. In this case, the carrier signal itself is present alongside the sum
and difference sidebands.