10.6

89Logic Pro Instruments
• Sharp: Two-pole analog-modeled filters.
• Smooth: Two- or multi-pole state-variable filters.
The three principal filter controls have standard functions for all filter types.
• Cutoff: Controls the filter cutoff frequency.
• Resonance: Controls the filter resonance or emphasis. Higher settings boost
frequencies in the immediate vicinity of the cutoff frequency.
• Drive: Allows the filter to be overdriven; the precise effect varies with each filter design.
Alchemy filter types: formant, notch, and peaking
A formant filter works like a bandpass filter with a potentially very narrow bandwidth. It is
designed to mimic a formant, or fixed resonance, such as those produced by the hollow
body of a guitar or by the shape of the vocal cavity (which is adjusted during speech to
produce different vowel sounds).
• Cutoff: Controls the resonant frequency of the formant.
• Amount: Controls the width of the band surrounding the resonant frequency. Low values
produce a narrow band, high values a wider one. Low resonance values may allow little
or no sound to pass through the filter.
A notch filter cuts a narrow band around a resonant frequency. The remainder of the signal
is affected minimally.
• Cutoff: Sets the frequency of the cut band.
• Amount: Controls the amount of attenuation.
A peaking filter boosts a narrow band around a resonant frequency. The remainder of the
signal is affected minimally.
• Cutoff: Sets the frequency of the boosted band.
• Gain: Controls the amount of boost. Higher values are generally the most effective.
• BW: Sets the bandwidth around the cutoff frequency.
Alchemy 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.
Alchemy offers three comb filter designs, each with its own character. The best choice is
very much a question of 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 modeled sound.