Filter block

Filter block

Axe-Fx III, FM3, FM9 — 4 blocks, 4 channels
VP4 — 4 blocks, 4 channels
AM4 — 1 block, 4 channels

Axe-Fx II — 4 blocks, no X/Y
FX8, AX8 — 2 blocks, X/Y

About the Filter block

A filter is a very versatile effect. Applications include:

• One-band equalizer
• Boost the input of an amp block
• Boost the overall signal level (i.e. for leads)
• High-pass (cut lows) or low-pass (cut highs) filter
• Envelope filter / Auto wah / Touch wah
• Find the resonant frequency of a guitar cabinet

Filter types

The Filter block provides these types:

1. Allpass
2. Auto-Wah
3. Band-Pass
4. Envelope Filter
5. Feedback Comb
6. Feedforward Comb
7. Highpass
8. High-Shelf
9. High-Shelf 2
10. Low-Pass
11. Low-Shelf
12. Low-Shelf 2
13. Notch
14. Null
15. Peaking
16. Peaking 2
17. Tilt EQ
18. Touch Wah

Auto Wah

The "Auto-Wah” type is based on the same “circuit” as the Envelope Filter (see below) but replaces the detector with an LFO.

FRACTAL AUDIO QUOTES

---

[1] If you like Wah with a Mix, just use the FILTER block. You have the option of LPF or BPF, adjustable Q, plus a ready-to-use Mix control. You'll need to set MIN and MAX in the Modifier rather than with knobs, but that's not hard.

Touch Wah

The "Touch Wah” type is similar to the Envelope Filter but uses a different type of detector and voltage-to-frequency converter. This type can be used to create interesting touch-sensitive filter sounds. It can also be used to replicate the Korg A3 Touch Wah sound (as heard in U2's Mysterious Ways) as follows:

• Set Mode to MIX
• Set Start Freq to maximum. Set Stop Frequency to minimum
• Start with a fairly high Attack Time, around 500ms
• Set Release Time to around 200ms
• Adjust Sensitivity to taste

Links:

• U2 - Mysterious Ways
• Leon Todd's Mysterious Ways tutorial

Lowshelf and Highshelf

FRACTAL AUDIO QUOTES

---

[2] […] A lowpass with "direct" signal mixed in is a lowshelf. A highpass with direct signal mixed in is a highshelf. In fact in the analog domain that's a common way of making low/high shelf filters.

It's intuitive as well. Take the direct signal and add/subtract some lowpass filtered signal. Now you have a bass boost/cut, i.e. lowshelf.

Lowshelf 2 and Highshelf 2

These filters 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.

FRACTAL AUDIO QUOTES

---

[3] The Lowshelf2 and Highself2 types are "analog" types and derived using "k + low/high pass".

Peaking 2

Many “classic” graphic equalizers use variable-Q designs which may be more familiar to some users as opposed to constant-Q filters.

FRACTAL AUDIO QUOTES

---

[4] Peaking 2 is constant Q. At +/- 12 dB they are the same. At other gains the Peaking 2 will have a wider bandwidth as the Q does not change.

Notch filter

FRACTAL AUDIO QUOTES

---

[5] Gain doesn't apply to a notch filter. Only frequency and Q are relevant.

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.

Feedforward comb, Feedback 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.

Allpass filterf

This is a multi-stage Phase Rotator with feedback. With feedback set to zero, it can be used to change the shape of transients. Using feedback causes constructive and destructive interference and can be used to create interesting tonalities. The Order can be set from 1 to 12 with progressively more phase rotation occurring. Attaching a modifier to the Frequency parameter can result in interesting chorus or wah effects. The red trace in the GUI is the phase response.

Envelope Filter

The Envelope Filter is based on the classic Mutron effect with some modern touches:

• The start and stop frequencies are freely assignable. Start can be lower or higher than stop. Simply set Start Freq higher than Stop Freq to sweep down.
• The Sweep Shape knob controls the mapping of the detector to the filter frequency. A value of 0.0 is a linear mapping. Higher values become progressively more nonlinear and make the response more “quacky”. The default value is commensurate with a typical consumer Vactrol.
• The detector attack and release times are programmable. Default values match the original pedal.
• The Emphasis control allows emphasizing the higher frequencies into the detector to even out the response when playing higher notes.
• The detector source is selectable between the block input or any of the hardware inputs. This allows placing the filter after an Amp or Drive block but using the instrument input as the source.
• A detector meter facilitates easy adjustment of the detector sensitivity to match your guitar and playing dynamics.

FRACTAL AUDIO QUOTES

---

[6] "Mix" mode combines the bandpass output with the dry signal.

Here are some demos of the 1972 Mu-Tron III pedal to match the model to:

• Pedal of the Day
• Soultron

User settings

Tips, tricks and troubleshooting

Factory presets

The Filter block is showcased in many factory presets. Search the Factory presets page for filter.

Slope

When working with filters and EQ, the slope is important. See this pic:

Design a preset for multiple guitars

Read Use Filter and Scene Ignore to adapt a preset to multiple guitars for more information.

Boost mids on 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.

Dynamic Distortion

Some filter types are also available in other effect blocks, such as the Dynamic Distortion block.

Sweep frequencies

Attach the global LFO controller or the LFO in the Filter block to the Frequency parameter to generate frequency sweeps, as demonstrated in many Factory presets.

Envelope filter (Auto Wah)

Before firmware 27 for the Axe-Fx III, Fractal Audio devices didn't provide a dedicated Auto-Wah effect block. A similar effect could be achieved by attaching the Envelope controller to a Filter or a Wah block. Attack is the time it takes to go from silence to maximum level. Release is the time it takes to drop from sustain level to silence after being released.

Try Factory presets such as: PSYCHADELIC CDUCK, FRENETICA, TRACK WAH.

Lof-fi filter sweep

Watch the video below for a lo-fi filter trick.

80's rock sound

FRACTAL AUDIO QUOTES

---

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.

The amp modelers let you obtain the same result using Pre EQ in the Amp block.

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.

Eric Clapton mid-boost

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

FRACTAL AUDIO QUOTES

---

[7] 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.

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.

Find the resonant frequency of a guitar cabinet

Read Finding the resonant frequency with a solid-state amplifier for more information.

Alternative to Boost in the Amp block

The Boost parameter in the Amp block boosts the signal at the input of the Amp block. If you rather have an boost with adjustable EQ, use a Filter block before the Amp block.

Alternative to Crossover block

There's no Crossover block in the FM3 and VP4. Filters can be used to achieve something similar. Check out the FM3 factory preset PULYFUZZ.

Alternative to a cabinet

A filter can be used to create an amp+cab-in-the room sound. Watch the video below.