Phat FX filter types in Logic Pro for iPad

Phat FX provides dozens of filter types.

Phat FX filter types: lowpass, bandpass, highpass

A lowpass (LP) filter passes the portion of a signal below a specified cutoff frequency and rolls off the portion above that frequency. A bandpass (BP) filter passes the portion of a signal occupying a band surrounding the cutoff frequency and rolls off the portions above and below that band. A highpass (HP) filter passes the portion of a signal above a specified cutoff frequency and rolls off the portion below that frequency.

There are multiple two-pole, four-pole, multi-pole state-variable and analog-modeled LP, BP, and HP filter designs in Phat FX, each with distinctive characteristics that you may prefer for a given purpose. The available LP, BP, and HP filter designs include Smooth, Edgy, Rich, Sharp, Clean, and Gritty variants.

Sharp: Two-pole analog-modeled filters.
Smooth: Two- or multi-pole state-variable filters.
Edgy: Two- or four-pole analog-modeled filters. Four-pole variants provide a steeper roll-off of frequencies beyond the cutoff.
Rich: Two- or four-pole analog-modeled filters. Four-pole variants provide a steeper roll-off of frequencies beyond the cutoff.
Clean: Bi-Quad filters. These filters have no Drive option.
Gritty: Two-pole filters designed to saturate heavily at higher Resonance and Drive settings.

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.

Phat FX filter types: notch and peaking

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.
Mix: 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.
Mix: Controls the amount of boost. Higher values are generally the most effective.
Resonance: Sets the bandwidth around the cutoff frequency.

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’re 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.
Drive: Controls the amount of feedback in the comb circuit.
Resonance: Controls 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.

Cutoff: 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.

Phat FX filter types: distortion

Phat FX filters offer several distortion effects.

Bitcrusher is a harsher-sounding digital effect.
Dirt is a classic tube distortion effect.
Downsampler is a lo-fi digital effect (similar to Bitcrusher but frequency dependent).
Grit is a transistor distortion.

The filter controls work as follows when the filter type is set to a distortion effect:

Drive: Controls the intensity of the distortion effect.
Mix: Controls the mix between clean and distorted signals. A 0% value results in the clean signal only. A 50% value results in an equal mix of clean and distorted signal. A 100% value results in the distorted signal only.
Cutoff: Sets the frequency for the Downsampler distortion type.

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