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Difference between revisions of "Filter block"

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=When to use a filter=
=When to use a filter=
A Filter is a very versatile effect. Possible applications include:
A filter is a very versatile effect. Possible applications include:
* One-band equalizer
* one-band equalizer
* Boosting the input of an amp block
* boosting the input of an amp block
* Boosting the overall signal level for leads
* boosting the overall signal level (i.e. for leads)
* High-pass or low-pass filtering
* high-pass or low-pass filtering
* Envelope filter / auto-wah
* envelope filter / auto-wah
* Finding the resonant frequency of your guitar cabinet
* finding the resonant frequency of your guitar cabinet
=Filter types=
=Filter types=

Revision as of 21:12, 16 April 2019

Available on which products

  • Axe-Fx III: 4 blocks
  • Axe-Fx II: 4 blocks
  • FX8: 2 blocks
  • AX8: 2 blocks

Channels or X/Y switching

  • Axe-Fx III: 4 channels
  • Axe-Fx II: no
  • AX8: X/Y
  • FX8: X/Y

When to use a filter

A filter is a very versatile effect. Possible applications include:

  • one-band equalizer
  • boosting the input of an amp block
  • boosting the overall signal level (i.e. for leads)
  • high-pass or low-pass filtering
  • envelope filter / auto-wah
  • finding the resonant frequency of your guitar cabinet

Filter types


Many “classic” graphic equalizers use variable-Q designs which may be more familiar to some users as opposed to constant-Q filters. In the Filter block this type is selected by choosing “Peaking2”.

Analog shelving EQ

“Lowshelf 2” and “Highshelf 2” recreate the analog shelving filters found on classic mixing consoles. These filters are somewhat quirky and exhibit “overshoot” which gives them a certain musical quality. Set Q between 0.5 and 0.707 to recreate those classic sounds, or experiment with Q for different amounts of overshoot. These filter types are great for getting that massive sound associated with passive equalization.

Tilt EQ

Tilt EQ is a slope filter that allows broad adjustment of the tone using just two parameters: Frequency and Gain. The Gain parameter sets the maximum gain of the filter relative to the center frequency. For example, a gain of 10 dB would set the maximum gain to 10 dB. The gain at the center frequency would be 0 dB and the minimum gain would be -10 dB, therefore a total of 20 dB of EQ would be applied.


"Gain doesn't apply to a notch filter. Only frequency and Q are relevant." source

FF Comb and FB Comb

FF Comb is a feed-forward comb filter and FB Comb is a feedback comb filter. Delay Time controls the order of the comb filters, higher values result in more closely spaced notches and vice-versa. Depth controls the intensity of the filter, higher values result in deeper notches/peaks and vice-versa.


Parameter Axe-Fx III Axe-Fx II AX8, FX8
Type yes
Frequency yes
Order yes
Q yes
Gain yes
Low Cut, High Cut yes
Pan L, Pan R yes
Delay Time yes
Depth yes
Phase Invert yes

Tips and tricks

Envelope Filter (Auto Wah)

Fractal Audio processors don't provide a dedicated Envelope Filter (Auto Wah) effect block. You can achieve this effect by attaching an Envelope to a Filter or Wah block.

Or try a factory preset such as the "Psychadelic Duck".

80's rock guitar sound

"This was a common technique in the 80's when tracking. If you have an Axe-Fx or other modeler with EQ options you can try it yourself. Put an EQ or Filter block before the amp. A parametric is best. Set the type to Peaking, Frequency to 1 kHz and Q to around 1 and gain to around 6 dB to start. Experiment with the parameters." source

Eric Clapton's mid-boost

To emulate Eric Clapton's mid-boost knob on his guitars:

"Use the Filter block. Since the max boost is 25 dB set the filter order to 4th which will give you a maximum of 24 dB. Set the type to Peaking. Set freq to 500 Hz. Vary gain and Q to taste." source

Clean boost

Set the Filter to "Null", set its Level to where you like it, put it at the end of the signal chain, and assign a switch. Now you have a simple, low-CPU, clean boost at your disposal.

Finding the resonant frequency of a guitar cabinet

  1. Put a Filter block after the Amp block.
  2. Set type to Peaking, Q to 5 or so and Gain to 10 dB.
  3. Start with a Frequency of around 50 Hz. Play some chugga-chugga and slowly adjust the Frequency until you hear and feel the cabinet resonate. You need to do this at loud volume level to notice it. Make a note of the frequency.
  4. Remove the Filter block and set the Amp block's Low Resonance to match.

Alternative to Boost in the Amp block

The Boost parameter in the Amp block boosts the signal at the input of the Amp block with 12 dB. If you rather have an adjustable boost, use a Filter block before the Amp block, set to "Null", with Level at the desired value.

Boston / Rockman sound

Put a Filter block in front of a Plexi amp model, select Peaking, set Frequency at around 800 Hz, Q at 0.707 and Gain at 12 dB. source

Boosting mids with FRFR amplification

A mid-boost can be help a guitar cut through the mix when using FRFR amplification. Try a Filter at the end of the grid, select Peaking, Frequency at 770 hz, Q at 0.35, Gain between 2 and 4 dB.