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Phaser block

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Available on which products

  • Axe-Fx III, FM9, FM3: 2 blocks
  • Axe-Fx II: 2 blocks
  • AX8: 1 block
  • FX8: 2 blocks

Channels or X/Y

  • Axe-Fx III and FM9 and FM3: 4 channels
  • Axe-Fx II, AX8, FX8: X/Y

About the Phaser block

Firmware Ares 12 for the Axe-Fx III, and corresponding FM3 and FM9 firmware, completely overhauled the Phaser block.


Firmware release notes:

  1. The Frequency parameter on the Basic page has been replaced by a "Manual" knob. It functions similar to the Flanger’s Manual control. To manually control the phasing set Depth to zero. The sensitivity of the Manual control is inversely proportional to Depth and the Manual control is disabled when Depth is at maximum.
  2. The Depth control mixes the LFO and Manual controls. When Depth is at minimum the phase shifter frequency is controlled entirely by Manual. When Depth is at maximum the frequency is controlled solely by the LFO.
  3. There are now separate Minimum Frequency and Maximum Frequency parameters. These set the minimum and maximum frequency when the Depth is at maximum and Manual is at minimum. These are updated when the type is changed.
  4. There are four "VCR Types” (Voltage Controlled Resistor). LINEAR is a simple linear mapping of LFO voltage to frequency. EXPONENTIAL gives an exponential response which can be more "musical" because the notches will move more linearly with the logarithm of frequency. JFET simulates the response of a Junction Field Effect Transistor when used as a variable resistor (as is commonly done in phaser pedals). PHOTOCELL simulates the response of a CdS photocell.
  5. The "Exponent" parameter controls the exponent for the EXPONENTIAL type. A value of 1.0 is "ideal" and results in the notches sweeping linearly with log(frequency). Higher values cause the frequency to dwell at higher frequencies and then decrease rapidly towards the lower frequencies. Lower values cause the frequency to dwell at lower frequencies.
  6. The VCR Bias parameter controls the bias point of the virtual VCR. A value of zero biases the VCR optimally. Negative values result in the VCR entering cutoff (infinite resistance).
  7. When using the PHOTOCELL VCR Type the attack and release times of the photocell can be configured using the Photocell Attack and Photocell Release parameters. Typical photocells used in phasers have an attack time of 5 ms and a release time of 35 ms but there is a bit of variation between photocell types. Shorter release times result in a “lumpier” response.
  8. The Feedback Point parameter now allows setting the feedback to any point in the phase shifter chain. A value of ‘0’ indicates prior to the beginning of the phase shifter chain. A value of ‘1’ indicates into the first stage and so on. Both positive and negative values of feedback are allowed. When adding feedback experiment with the Mix value. Increasing the Mix can achieve rich, hybrid vibrato/phase sounds.
  9. Up to 12 phase shift stages are allowed in multiples of two stages. As the number of stages is increased more notches occur in the spectrum. Experiment with the Minimum and Maximum Frequency values to move the notches in the spectrum.
  10. Most of the models are configured for mono operation with the LFO Phase set to 0.0. This is suitable for use before an Amp block. Placing the Phaser block after the Amp and Cab blocks allows for stereo phasing. Use the LFO Phase parameter to vary the phase of the right channel LFO in relation to the left.
  11. The Barberpole algorithm has also been completely reworked yielding more convincing “infinite phasing”.
  12. NOTE: Due to the comprehensive nature of the changes any existing presets will have the Phaser block reset to default values for the selected type. This can change the sound of existing presets that use the Phaser block and those presets should be auditioned and adjusted accordingly.

Phaser block diagram

Phaser block.png

Phaser types

Barber Pole
 Like the Shepard tone, this phaser type creates the illusion of a never-ending upwards cycle. Works best when placed at the end of the signal chain.
Block 90
Based on the MXR Phase 90 and Phase 45 pedals. The 45 uses subtle two-stage phasing, while the 90 type uses more pronounced four-stage phasing.
Script refers to the early MXR pedals which had the name printed in script font. They feature a more subdued sound with higher headroom and greater clarity.
The later Block pedals are more modern and rely on internal feedback to create light harmonic distortion and give the effect a more accentuated swoosh.
The Stripe 90 type is based on the MXR EVH Phase 90, an EVH-specific version of the Phase 90.
A photograph of EVH's phaser and flanger settings might help you replicate his sound.
Borg Phaser
Based on the black-with-orange Korg PHS-1, and models the Speed and Intensity controls on the original pedal.
The original manual is available online.
Classic Vibe
The Uni-Vibe effect is a type within the Phaser block. The Classic Vibe type is based on the Fulltone Deja-Vibe.
Put the effect before the Amp block for best results, connect a pedal or switch to the Rate parameter to control speed, and turn Mix to 100% for Vibrato mode.


[1] It sounds exactly like the pedal it was modeled after, a Fulltone Deja-Vibe. That, however, may not be your idea of what it should sound like. If you are using Line 6 as a reference, their effects are often exaggerated caricatures of the real thing. Our models are more subtle and strive for accuracy.

[2] The Axe-Fx model is based on the Fulltone.

[3] Yeah, the vibe is fun. I bought a Fulltone Univibe clone and used that to verify the new model.

Check out the High Landrons preset now.

[4] Turn Mix to 100% for Vibrato mode.

[5] It's so hard to make a good UniVibe clone. You gotta get the photocells just right. If they're too slow it won't be lumpy and drippy enough. Too fast and it will thump. Use anything but a photocell and it just sounds terrible.

[6] A really cool feature is the new "Bulb Bias" parameter. You can adjust the quiescent current of the virtual light bulb to control how "lumpy" the sweep is.

Rotovibe settings:

[7] Here's a quick and dirty starting point.

Start with the Classic Vibe model in the Phase block.

Reduce the Mix to 50% for a bit less pitch warble

One the More page of the Phaser block, try these to even out the sweep:

Type: Photocell
Bias: 0.25
Exponent: 1.0
Attack: 10ms
Release 10ms

From there, assign a pedal to the rate parameter with Min around 1 Hz and Max around 6 Hz or so.

To my ears it tends to sound the best with the depth turned down a bit at higher settings, so one way to do that is to assign the same pedal to the depth parameter as well. Set Min to around 5 and Max to 10 and then Swap the Start and End values to 100% and 0% respectively. That will make the depth go down as the rate goes up and you end up with a bit more even sounding rate range.

Sounds decently close into a cranked JCM800 style amp.

See these links for more information:
Digital Mono
Digital Stereo
FAS Vibe
Fractal Audio's custom Uni-Vibe version.
Mutated Twin-Phaser
Based on the multifunctional stereo Mutron Bi-Phase.
To achieve a similar sound in earlier firmware, set the Phaser to 6 stages.
For a 12-stage mono Mutron: set Order to 12 and LFO Phase to 0.
The manual is available online.


mjahoger said:
Is there a way to have the bi-phase in series? Zappa used to have Phaser B wired into Phaser A for the Black Napkins tone, creating a 12 stage Phaser in mono with a synced LFO.

[8] Yes. Begin with the MUTATED TWIN PHASE type. Set ORDER to 12 and set LFO Phase to 0.

Naughty Rock
Based on an Electro-Harmonix Bad Stone phaser that uses six stages as opposed to the more famous four-stage EHX Small Stone phaser, it models the original controls: Rate, Manual Shift, Feedback, Auto/Manual.
See Premier Guitar's Review for more information.
Script 45
See Block 90 above.
Script 90
See Block 90 above.
Stereo 8-Stage
Stripe 90
See Block 90 above.
Based on the large chrome Morley Pro PFA Phaser, with a treadle mechanism.
Controls modeled from the original pedal:
  • Phase Travel, which controls the depth/amplitude of the modulation, i.e., the size of the range in which the effect sweeps.
  • Center, which sets the position of the effect when the LFO is in the center position or controls the effect when the LFO is switched off
  • Harmonic Emphasis, which sets the amount of affected signal fed back into the effect, for a stronger effect.
Ultra-Super-Mega Phaser
Fractal Audio's custom phaser type.
Virtuoso Phaser
Based on the venerable Maestro MP-1 phaser, made by Bob Moog. This is a six-stage phaser, assumed to be the pedal that Jimmy Page used on Led Zeppelin's Nobody's Fault But Mine.
Original controls modeled are Balls (depth) and Speed.
The Technical service manual is available online.

Mono or stereo

The Phaser defaults to mono to prevent phase problems when used before an Amp block. To make it stereo, change the LFO Phase setting and place it after Drive, Amp and Cab.




[9] Phasers cause notches in the spectrum which can reduce the apparent volume. It depends on the frequency content. Overdriven sounds have more content and will be affected more. The Level knob allows you to compensate for this.



[10] Real phaser pedals never achieve exactly 50%. In my testing I found that a higher mix can sound better, especially when using feedback.


The Order parameter lets you change the number of phaser stages.



[11] There is no feedback on a Script 90.

LFO Bypass Reset

If LFO Bypass Reset is set to anything other than Off, LFO will be reset to the selected phase whenever the block is bypassed. This allows synchronizing the sweep to engaging the effect.

Tips, tricks and troubleshoooting

Factory presets

The Phaser block is showcased in many factory presets. Search the Factory presets page for phaser.

Step phaser

Current firmware:

To create a stepped phaser, set Depth to 0, attach the Manual control to the Sequencer. You can use the Min and Max values in the controller as well as the Minimum Frequency and Maximum Frequency settings on the Phaser block to tune the effect.

Or use the LFO Quantize parameter.

Earlier firmware:

To create a stepped phaser, set Depth to 0, attach Frequency Start to the Sequencer, set Min and Max and adjust the Sequencer faders.

Phaser / Uni-vibe effect

You can also use the Ring Modulator as a phaser or uni-vibe.

MXR Phaser 100

This phaser has not been modeled.


[12] You can get pretty close with a 10th order phaser. I could add a parameter that selects the number of stages to modulate but I don't think it's necessary, simply reduce the sweep depth.

Envelope-driven phaser

Use the Envelope follower to create a touch-sensitive phaser, as demonstrated in this FM3 factory preset: TOUCH PHASE FM3

Prevent the thump

Auto Input Impedance can can cause a low-frequency thump when engaging the Phaser. Read Input impedance for more information.