Always consult the official Owners Manuals first

Controllers and modifiers

From Fractal Audio Wiki
Jump to navigation Jump to search

About controllers and modifiers

Controllers are explained in depth in the Owner's Manuals. They allow real-time control over parameters and therefore over sound.

Some examples are:

  • an expression pedal is an external controller that works with the Wah block.
  • an external on/off switch is an external controller that can turn an effect on and off or taps the tempo.
  • an envelope follower is an internal controller that enables fade-ins.
External controllers 
These are a gateway between the device and another external hardware device such as a pedal, switch, or MIDI device. The Axe-Fx III, FM3 and FM9 support 16 external controllers per preset.
Internal controllers 
Internal controllers generate data within the device, which in turn change parameter values. The envelope follower, LFO, and ADSR are examples of internal controllers. Use the Controllers block to adjust their settings, per preset.
Scene controllers 
See Scene controllers for more information.
Control Switches 
See Control Switches for more information.
Refer to the modifier menu, explained in the Owner's Manuals. Placed between the internal or external controller and the parameter which is being "controlled", the modifier menu provides additional parameters to modify the data.

The Axe-Fx III, FM3 and FM9 support 24 modifiers per preset.

Controllers: Channels or X/Y

  • Axe-Fx III: 4 channels
  • FM3: 4 channels
  • FM9: 4 channels
  • Axe-Fx II: no
  • FX8: no
  • AX8: no

Internal Controllers, including Tempo, are regarded as a block in the Axe-Fx III, FM9, and FM3, albeit not a block that can be placed on the grid. This block has four channels.

Internal controllers

Current firmware provides internal controllers with four different sets of settings per preset, through Channels.

Also, some of the ambient blocks, such as the Multitap Delay block, have built-in controllers, such as an envelope follower on the input which allows creating swell effects without having to use an internal controller.

See the Owner's Manuals for more information.


Five internal controllers generate control data without the help of an external device:

LFO generates control signals as familiar wave shapes or random signals. Each LFO outputs two signals, A and B.


Ares firmware 12 and later (and corresponding FM3 and FM9 firmware):

Added "Astable" type to LFOs. This simulates an astable Op-amp Multivibrator as is commonly found in effect pedals. "Beta" controls the shape of the LFO. High values approach a square wave while low values approach a triangle wave.

Firmware 23 and later (and corresponding FM3 and FM9 firmware):

The "Astable Beta" parameter for the LFOs has been renamed "Shape" and now controls the shape of the LFO for all types except Square and Random.

[1] You can start a sweep, ramp, etc. from a known value. When you stop the LFO it resets the function argument to zero. The output is then, for example, sin(0) = 0. The random type doesn't have a value associated with an argument of zero so it doesn't reset.

Generates control patterns by looping through 2-32 stages.
Envelope generators with ATTACK, DECAY, SUSTAIN and RELEASE parameters (thus ADSR).
 The time it takes to go from silence to maximum level.
 The time it takes to drop from maximum level to the sustain level or silence.
 The volume of a note while holding it.
 The time it takes to drop from the sustain level to silence after being released.

Firmware 19.01 and later for the Axe-Fx III (and corresponding FM3 and FM9 firmware) added a Type control to ADSRs. The default, EXPONENTIAL, is an analog-style where the ADSR has an exponential attack/decay. LINEAR selects a linear attack/decay.

Envelope Follower 
Converts input levels to control signals, responding variably to playing dynamics. In comparison, the ADSR envelope generator always creates the same control signal, but only triggers when you play hard enough. Use Envelope to create an Auto Wah: attach Envelope to the Control parameter in the Wah block and hit the note hard for more effect, hit it soft for less effect.
Pitch detector 
Analyzes the pitch of your playing and outputs a low value for low notes and a high value for high notes.

Envelope and Pitch only detect signals at the front input of the Axe-Fx II and AX8, and Input 1 left rear (Axe-Fx II). The FX8 lets you adjust this for POST-only setups. The Axe-Fx III, FM9, and FM3 have expanded possibilities and their Pitch block(s) have their own detectors.

For more information see these pages:

External controllers

Through external controllers you can manipulate effect parameters with a pedal, switch, dial, etc.

The Axe-Fx III, FM3 and FM9 support 16 external controllers per preset.

Engage and bypass an effect through an external controller

You can attach a controller to the effect's Bypass (Mode) parameter. This will not change the bypass mode, but it'll act as an On/Off switch for the effect block. The side-effect is that you can no longer engage or bypass that effect manually by editing the preset. The On/Off state is determined by the external controller, exclusively. Current firmware provides separate Bypass and Bypass Mode parameters.

Set the state of a disconnected external controller (INIT VALUE)

Setting the initial state of an external controller is important to prevent issues when that controller is not connected. For example, you are using a controller (a pedal) to control the overall volume. To make sure that the output volume is 100% when the pedal is NOT connected, set the controller's initial state to 100% (MIDI > Initial Value). Initial Value settings apply only to external controllers, not to pedals that are directly connected to the device.

The AX8 and FX8 detect if a pedal is not connected and set the controller's initial state at 100% automatically. The Init Ctrl value will be bypassed.

MIDI CCs for external controllers

Axe-Fx III and FM and FM3 – assignable in the MIDI/Remote menu

Axe-Fx II – External controllers 1-12 correspond with MIDI CCs 16 - 27

AX8 – External controllers 1 - 4 are assigned to Pedal 1 - 4 by default

FX8 – External controllers 1 and 2 are assigned to Pedal 1 resp. Pedal 2 by default



What does Auto-Engage do

The Auto-Engage modifier parameter allows engaging and bypassing effects automatically. Example: rocking an expression pedal will engage and bypass the Wah block automatically without having to press a switch first, like an optical Wah pedal.

Configure Auto-Engage

You can make Auto-Engage kick in depending on the pedal's position, or the speed with which you rock it. "Position" depends on the OFF VAL setting.

Firmware release notes:

[2] Added speed (SPD) vs. position (POS) options to Modifier Auto-Engage parameters. The SPD options engage the effect when the controller changes more than 5% in any 20 ms interval (as before). The POS options engage the effect when the controller value is 5% greater than or less than the Off Value (depending upon whether the Off Value is less than or greater than 50% respectively). For example, setting the Auto-Engage to SLOW SPD will bypass the effect when the controller value is less than, say, 5% (default). To engage the effect the controller (foot pedal) must be moved more than 5% in a 20 ms interval. This requires that the pedal be moved somewhat rapidly and prevents the effect from engaging erroneously if the pedal droops. Setting the Auto-Engage to SPD POS will bypass the effect in the same manner but the effect will engage when the controller exceeds 10% (5% + 5%) regardless of the rate of change.


[3] The on value is 5% higher than the off value. This is by design. It's called hysteresis and it's a common technique used in many "bang-bang" controllers, i.e. thermostats. This is to prevent chatter at the threshold.

OTHER QUOTES Forum member Bakerman:

Both auto-engage types need to go into the off zone (determined by Off Value) to disengage. Position/speed really only changes the conditions to engage the block. "Speed" type requires a certain rate of change instead of simply reaching some value.

To turn an expression pedal into a virtual "toe switch": set OFF VAL to around 90% and Auto-Engage to Medium or Slow.

Using Auto-Engage with scenes

When switching scenes while the effect is still engaged, the effect will also be engaged in the new scene. In other words, an Auto-Engaged effect survives scene switching, even with Scene Revert set to ON.

Using Auto-Engage with the editor

Auto-engaging an effect in the Axe-Fx II, AX8 and FX8 will not be visible in the editor for technical reasons. In other words, the block won't be un-bypassed visually. To see the actual state of the block, refresh the editor.

Alternative to Auto-Engage

Auto-engaging an effect can cause an hickup in the audio when engaging the effect, for example when using the Pitch block to create a Whammy effect. To avoid this, use modifier settings like these instead of Auto-Engage:

  • Auto-engage = off
  • Min = 100
  • Max = 0
  • Start = 60
  • Mid = 0
  • End = 49.8
  • Slope = 100
  • Scale = 10
  • Offset = -100

These settings pass the unmodified signal at the heel-down position and switch to 100% processed sound when moving the pedal while retaining the expression pedal's regular functionality. Note that this only works with effects where the heel-down position sounds like the unmodified direct tone and which have a Mix parameter. This rules out the Wah block.

Another alternative is to use the approach shown in the DEVY TOWNSEND factory preset, where the hiccup when engaging is avoided.

PC RST (Program Change Reset)

This parameter determines whether a modified parameter will be reset to its stored value when switching presets, or stay at its current value (survive preset switching).

For example, you have an expression pedal assigned to a Level parameter. You set the pedal halfway and then switch presets. PC RST determines whether the new preset maintains the pedal position and sets Level accordingly, or sets Level at the stored value of the preset, regardless of the pedal's position. If it's ON, the stored value will be used, until the pedal is moved.


[4] […] The new value must be 5% different than the previous value, otherwise whatever value the pedal is at, will immediately override the "PC RST" value. The idea is that the parameter is set to a value when you recall the patch. You then have to move your pedal a bit (5%) to regain control of the parameter. This is done for two reasons:

  1. Many MIDI controllers send the state of their expression pedals along with the PC message. If the behavior weren't as described, the stored parameter value wouldn't stick.
  2. Many MIDI controllers have "noisy" expression pedals where the value tends to bounce around a little. This prevents the stored value from being lost.

Damping and Attack/Release

Damping determines how long it takes to move the parameter between values.

Damping provides separate Attack (up) and Release (down) parameters. This means that damping up and down can be set at different times. Also, the maximum damping time has been expanded.

Also, in firmware 19.01 and later for the Axe-Fx III (and corresponding FM3 and FM9 firmware) you can select between:

  • Exponential damping (default: classic damping style where the modifier value has an exponential attack/decay
  • Linear attack/decay

The Axe-Fx II, AX8, and FX8 allow a maximum damping time of 1000 ms.

Update rate

Ares firmware and later:

This selects the rate at which the modifier updates the target parameter. For most applications a slow rate is sufficient. That's always the case with external controllers.

Under some circumstances, a slow or medium rate combined with an internal controller may cause “zipper noise”. Increasing the rate will reduce the noise. Note: higher update rates increase background CPU usage and should only be used when absolutely necessary.

Modifier curves

Read the Owner's Manual for more information and diagrams.

applies gain to the modifier curve, allowing the user to create steeper or shallower curves (vertical). Use this to optimize your pedal.
allows shifting the curve up or down the Y-axis.
 introduces an "S"-shaped curve.

Turning up the Scale will ensure that the Control value reaches maximum even if the pedal doesn't. [5]


Admin M@:

  • Create a Whammy effect, reaching an octave at toe-down, with extra "play" at the top: Pitch CONTROL; SCALE 1.089; OFFSET 10.0
  • Make the Auto-Engage "bump" disppear (true bypass at heel-down): Pitch MIX; Start 40; Mid 100; End 55; Slope 0; Scale 10; Offset 100
  • Make a modifier go straight from MIN to MAX at toe-down: START 0; MID 0; MAX 60; SLOPE 0; SCALE 10; OFFSET -100
  • Create a Log taper in a modifier menu: set "Mid" in the modifier menu to 20%. Adjust the Slope to avoid the dead zone


Dual source modifiers

The Axe-Fx III allows assigning a second source to a modifier (dual source modifiers), i.e. to use two Wah pedals.

These are not supported on the FM3 and FM9.

Modifiers and Channels

Current firmware lets you assign a controller to a parameter and apply that either to a single channel or to all channels in the modifier menu. This allows flexible use of a modifier, especially across scenes. Note that you can only select "single" once, meaning that you can NOT assign a separate controller to each of the four channels.

Multiple controller settings within a single preset are possible, because the Control block has 4 channels.

Control Switches

This applies to:

  • FM3, FM9 and FC controllers
  • AX8

Instead of an internal or external controller, a modifiable parameter can be assigned to a Control Switch (CS). The CS can then be controlled with an onboard switch or FC controller. This allows controlling a function like Input Boost in the Amp block with an onboard switch.

The state of the Control Switch is saved per scene.

Control switches can also be used to send MIDI commands. Read MIDI for more information.

Control Switches are documented in the Owners Manuals for the FC controllers for FM3, FM9, and AX8.

Axe-Fx III

The Axe-Fx III provides six Control Switches (CS). The Control Switch can operate as a latching or momentary switch.

The state of a CS is stored per scene: On, Off, or Last. Last, which is the default, leaves the switch state unchanged when you change to a scene with this setting. The per scene settings can be accessed from the CS PER SCENE page in the Controllers block.

Control Switches can be made part of a mutually exclusive group. This means that engaging one will bypass the others.

The Control Switches also let you transmit MIDI at will by pressing the switch when using an FC-6 or FC-12 or FM3. This doesn't depend on a preset change or scene change. Up to four MIDI commands (PC or CC) can be transmitted.

FM3 and FM9

See Axe-Fx III above.


The AX8 has provides two Control Switches, which can be assigned globally or per-preset like any other footswitch block from the main Footswitch (FS) page.

To set up a Control Switch footswitch:

  1. On the Footswitch (FS) page, use the NAV and A knobs to assign CS1 or CS2 to footswitch 1 – 8
  2. Add a modifier to the desired effect parameter, setting CTRL SW1 or CTRL SW2 as the source
  3. Adjust the modifier to work as desired

To set initial values for a Control Switch:

  1. From the main FOOTSWITCH (FS) page of the AX8, page right to the CONFIG page
  2. Select the CONTROLLERS option and press <ENTER>
  3. Page to the CONTROL SWITCH (CTRL SW) page
  4. Set the initial value of each switch for each scene to either ON or OFF

For more information see Why use Control Switches vs. Scenes.

Manual controls

Firmware Ares 6 and later for the Axe-Fx III brought back the 5 manual controllers from the Axe-Fx II firmware.

These are accessible in the Controllers block and/or Performance Pages, and can be used as modifiers for real-time manipulation of parameters from the front panel, without needing an expression pedal, MIDI device, or other controllers.

CPU usage

Using controllers increases CPU usage slightly. For example, when you move a pedal which is assigned to a parameter, it'll send control data which will increase CPU usage temporarily.

Tips, tricks and troubleshooting

Factory presets

Search the Factory presets page for controller to see examples of usage of an external and internal controllers.

See which parameters have a controller assigned

To see if and which controllers are used in a preset, go to the Controllers and scroll to the last tab page.

You can do the same in the software editor. Press Enter after selecting a controller on the Mods page to open its Modifier menu, except for CONTROL modifiers. Exit or Control will return from a modifier menu to the Mods menu.

Global blocks

Modifier settings and controller assignments are not saved with Global blocks.

Using controllers and modifiers in a DAW

Forum thread

Unable to type Min/Max modifier values in the software editor

The software editors do not allow typing values in the Min/Max fields of a modifier menu, for technical reasons. Use the mouse instead.