Always consult the Owners Manuals
From Axe-Fx II Wiki
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Filter: supported by which Fractal Audio products
- Axe-Fx III: 4x.
- Axe-Fx II: 4x.
- FX8: 2x.
- AX8: 2x.
Filter: X/Y-switching or channels
- Axe-Fx III: 4 channels.
- Axe-Fx II: no.
- AX8: yes.
- FX8: yes.
When to use a filter
A filter is a very versatile effect. Possible applications include:
- One-band equalizer.
- Boost the input of an amp block.
- Boost the overall signal level for leads.
- High-pass or low-pass filter.
- Envelope filter / auto-wah.
- Find the resonant frequency of your guitar cabinet.
The Owner's Manual also explains 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 the “Peaking2” type.
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 the Q between 0.5 and 0.707 to recreate those classic sounds or experiment with the Q for different amounts of overshoot. These filter types are great for getting that massive sound associated with passive equalization.
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
Tips and tricks
Envelope Filter (Auto Wah)
Fractal Audio processors don't have 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 the "Psychadelic Duck" preset (Axe-Fx II).
Eric Clapton's mid-boost
To emulate Eric Clapton's Mid-Boost 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
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.
Find the resonant frequency of a guitar cabinet
- Put a Filter block after the Amp block.
- Set the type to Peaking, Q to 5 or so and Gain to 10 dB.
- 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.
- 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 a adjustable boost, use a Filter block before the Amp block, set to "Null", with Level at the desired value.
Reproduce the 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
Boost 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.