Drive block

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The Drive block

Available on which products

• Axe-Fx III: 4 blocks
• FM3: 2 blocks
• Axe-Fx II: 2 blocks
• AX8: 2 blocks
• FX8: 2 blocks

Channels or X/Y switching

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

About drive modeling

Yek's Guide to the Fractal Audio Drive models

Forum member Yek has written a guide (PDF) that covers all the models in detail. Click on the image below.

Pictures of the modeled pedals

Gallery of modeled pedals, by forum member MDProd

Modeling improvements in firmware Ares

"The drive block in the III uses a higher oversampling ratio and double-precision filters in some places compared to the II." source

Firmware Ares 3.02

This firmware introduced major improvements to modeling of drive pedals. Drive models based on op-amp and diode clipping topologies were been completely overhauled. This is referred to as: FASPICE. This includes all types based on the Tube Screamer circuit.

Important: these changes result in significant changes in sound, gain and level. Tips and tricks for Drive blocks prior to firmware 3.02 may not apply anymore. Also, demos and tutorials may not represent the current tone anymore.

Firmware release notes:

"Drive models based on op-amp and diode clipping topologies have been completely overhauled in firmware 3.02 and later.

For many types there is now a “Dry Gain” control. This parameter controls the amount of “dry” signal mixed with the “wet” (distorted) signal. For a Tube Screamer-based model this will default to 100% due to the topology. For other types this will default to 0. Values up to 200% are allowed. Note that the dry data is added before any tone controls and therefore is not exactly equivalent to a mix but rather replicates the behavior of analog circuits.

Drive types based on op-amp and diode clipping circuits now allow control over the type and quantity of diodes in the positive and negative polarity. For example, the user can select (2) 1N34A diodes for positive signal polarity and (1) red LED for negative. Experiment with the various diode types and quantities to obtain new and unique sounds.

The Basic GUI page now reflects only the controls found on the actual pedal. In cases where the actual pedal does not have any tone controls a simple Tone control is included for convenience."

The tone circuits of ALL drive types have been updated in firmware Ares 3.02 and later, and all models have been rematched to the original pedals. source source

The changes do not apply to the input boosts in the Amp block. source

More about FASPICE:

"New Drive block algorithm (FASPICE) implemented and working." source

"I've "cracked the code" on drive pedals and figured out a way to do a SPICE simulation in real time without using gobs of CPU. It's so simple I can't believe no one ever thought of it before but none of the papers even approach anything resembling the technique. This will bring "Ares" level modeling to the Drive block." source

"This algorithm applies to a particular set of circuits that incorporate diodes as a nonlinear component. SPICE modeling is particularly slow when modeling diodes due to convergence issues. However the diodes in drive pedals are used in such a way that there's a trick that can be employed to dramatically decrease the amount of CPU needed to simulate the circuit." source

"It normally takes a lot of CPU power to do a real-time simulation. The amp block uses an entire dedicated DSP. To do even a simple distortion pedal would normally require huge amounts of CPU. But I stumbled upon a simple trick that reduces it dramatically." source

(picture) "See the two diodes, D1 and D2? The type and quantity of these diodes (among other things that I can't reveal) affect the tone. D1 is the "negative" diode. It conducts when the voltage is negative. D2 is the "positive" diode. It conducts when the voltage is positive. In this schematic the diodes are listed as 1N34A but in the original Distortion+ they were actually 1N270. If you select the Plus Dist model and go to the last page in the UI you'll see the type of diode is 1N270. You can change the type and quantity which will change the distortion characteristics.

1N270 and 1N34A are Germanium diodes. They have a greater reverse saturation current (Is) and, hence, a lower forward voltage for a given current. This means they clip sooner. Silicon diodes, i.e. 1N4148, 1N916, etc. have a lower Is and a greater forward voltage. LEDs have yet a greater forward voltage (smaller Is).

This new firmware has 16 diode SPICE models that I collected from various sources that you can play with. 1N914 are often substituted for 1N4148 and vice-versa but they are slightly different so I included both. The original Tube Screamer had 1S1588 which, to my ears, are much different (better) sounding than 1N914 which are used in the newer Tube Screamers." source

Wikipeda: "SPICE ("Simulation Program with Integrated Circuit Emphasis") is a general-purpose, open-source analog electronic circuit simulator. It is a program used in integrated circuit and board-level design to check the integrity of circuit designs and to predict circuit behavior."

Firmware Ares 10

Firmware release notes:

• Improved Drive block. New diode modeling algorithm improves clipping accuracy especially for diodes with higher saturation currents, i.e. 1N270 and other germanium types.
• Added D9E and D18 diode models to Drive block. These are Soviet germanium diodes valued for their smooth distortion characteristics.

"Firmware 10 uses new "FASPICE XD" modeling in the amp and drive block. It requires a bit more CPU but the accuracy is far better. I figured out a way to ensure that transcendental equations are always stiffly stable and converge in a fixed amount of time. Significantly faster and at least as accurate as trapezoidal, modified trap, gear, etc. algorithms. It dampens numerical ringing without the side-effect of damping actual circuit ringing. Once you see how it works it seems hard to believe that no one has thought of it before but I can't find a single paper or article that uses the technique. The only drawback is that frequency response is limited to about 1/2 Nyquist but since we oversample that's irrelevant. So that's why you get the "amp feels like it's going to explode" but without the noise and artifacts." source

The affected Drive models are: (source)

• Rat
• Super OD
• T808 OD
• Fat Rat
• Plus Distortion
• Full OD
• Blues OD
• Shred Distortion
• M-Zone Distortion
• BB Pre
• Eternal Love
• Esoteric ACB
• Esoteric RCB
• Zen Master
• FAS LED-Drive
• Ruckus
• FAS Boost
• Timothy
• Tone of Kings
• Heartpedal 11
• Jam Ray

Firmware Ares 12

The Drive block's EQ now supports placement pre- or post-distortion.

Firmware Ares 13

(release notes) "Improved Drive block modeling. New algorithm uses a novel solution to solve the nonlinear ODE of a diode clipper with memory (i.e. a capacitor). The accuracy of the diode I-V curve is also greatly improved. This new algorithm has the accuracy of implicit iterative solutions with speed rivaling explicit solutions. CPU usage is only slightly increased vs. the previous algorithm. Note that many of the Drive models will now behave differently and presets should be auditioned. The behavior of the tone controls in some models has also changed. Of note are the Timmy models where the tone controls are now faithful to the actual pedal and decrease bass/treble when turned clockwise.

The Drive block now features a “Bass Response” control for types based on the Rat, Tube Screamer and various derivates. In some models this is duplicated on the Basic page as it is the Bass/Voice/etc. control (and renamed accordingly). This function was previously provided by the Low Cut control. The Low Cut control is now a separate control that allows adjusting the input highpass frequency. Existing presets will automatically be updated with the new default value for the Low Cut control.

Added Bias control to GUI of all Drive block models."

More information

Drive block and CPU usage

The Drive models take up various amounts of CPU. The numbers are listed in Yek's Guide to the Fractal Audio Drive models (PDF).

CPU usage is amplitude dependent on the Axe-Fx II, AX8 and FX8. This means that CPU usage will change when you hit the strings (even with the Drive block in bypassed state). This does not apply to the Axe-Fx III and FM3.

Drive models in firmware Ares 3.02 and later require somewhat less CPU (1-2%) than before. Diode-based models in firmware Ares 13 and later require more CPU.

Drive types as input boosts in the Amp block

Some of the Drive models are available as input boosts in the Amp block. Read this: Input Boost

Drive block controls

"The Tone control works the same as the modeled pedal. The Bass, Mid and Treble controls are a generic EQ that can be used in addition to the Tone control to further shape the sound." source

In firmware Ares 3.02 and later, the basic GUI page reflects only the controls found on the actual pedal. In cases where the actual pedal does not have any tone controls, a simple Tone control is included for convenience.

(firmware Ares 13) "The Drive block now features a “Bass Response” control for types based on the Rat, Tube Screamer and various derivates. In some models this is duplicated on the Basic page as it is the Bass/Voice/etc. control (and renamed accordingly). This function was previously provided by the Low Cut control. The Low Cut control is now a separate control that allows adjusting the input highpass frequency. Existing presets will automatically be updated with the new default value for the Low Cut control."

Fuzz, buffers and impedance

Many fuzzes depend on a direct connection between the guitar pickup and the input of the pedal. A modeler gets in the way because its input is always buffered. Thuis means that a modeled fuzz will react differently than the actual pedal.

"The Fuzz in the Axe-Fx reacts as though there is a buffer in front of it (because there is). It's a limitation inherent to all modeling products. I modeled it using a nominal source resistance. I forget what I used for the source resistance but it was probably around 100K ohms. To really simulate it you would need a controller to simulate the changing output impedance of the guitar." source

"You can simulate the effect of a guitar into a Fuzz-Face using the Input-Z feature." source

"The problem is that the signal is buffered and there is no way to model the interaction of the pickups with the circuit." source

(firmware 4.00 for the Axe-Fx III) "Duplicating the behavior of a fuzz pedal requires that the pedal be the first non-bypassed block following the Input 1 block and the input block impedance must be set to Auto since fuzz pedals load down the guitar’s pickups."

Forum member AustinBuddy recommends setting Input Impedance to 90K in presets which have a fuzz model as the very first (non-bypassed) block. This doesn't apply to processors with a fixed input impedance.

Read this: Input impedance

Tips and tricks

Tighten the tone with a Drive block or Input Boost

A Drive block before the Amp block, with minimal gain, will tighten the low end of dirty amp tones. It also allows turning down gain in the Amp block. This works well in particular with Tube Screamer-based Drive types.

Alternatively, use a PEQ block, set to Blocking, copying High Cut and Low Cut values from a favorite Drive type. This will apply the same coloring as the drive, without the gain and CPU usage.

Firmware Ares also provides Input Boost types in the Amp block itself, see above.

Turn an Amp block into a Drive

Insert a second Amp block before the main Amp block, set its Supply SAG to zero ("p.a. off") to switch off power simulation, and you have changed the amp model into a preamp / drive model. Set the main Amp block to a fairly clean tone for best results. Try this with these models: Euro Blue/Red/Uber, Friedman BE, Dizzy, 5153.

More information:

• forum discussion
• Leon Todd's tutorial

Add gain to high single notes with the Pitch Detector

Attach Pitch (internal controller) to the Drive parameter and use Slope in the modifier menu to fine-tune. This will add gain to single notes when played high on the neck.

More information:

• Forum discussion
• Leon Todd's tutorial

Use a Drive type to warm up or soften a Synth sound

A Drive type, especially the RAT, is often used (in front of the Synth block) to warm up or often a synth tone.

Use Tape Distortion to add vintage flavor

The Tape Distortion, either before or after the Amp block, can add a vintage flavor to the sound.

Emulating other drives and devices

Note: because of ever evolving firmware, the suggested settings in the links below may not be accurate.

• Currently there's no Fractal Audio model of the Klon Centaur boost/overdrive pedal. Here are ways to approach its sound:
  • Camilo Velandia matches a Klon Centaur
  • AustinBuddy's suggested settings
  • Yek replicates the EHX Soul Food, a Klon clone
  • Leon Todd's AA Workhorse settings (a Klon clone)
  • PEQ settings to simulate a Klon: band 1 Shelving2, 150 Hz, 0.707, -12, band 5 Shelving2, 2253 Hz, 0.707, -12, Level 1.5
• Solo Dallas Schaffer Replica pedal, more information
• Maxon OD808
• Xotic BB preamp AT
• Xotic EP Booster
• Roger Mayer Axis Fuzz
• Boss HM-2

Parameters

Parameters table

Parameter	Axe-Fx III / FM3
Type	yes
BASIC + EQ 1
Drive	yes
Tone	yes
Low Cut, High Cut	yes
Bass, Mid, Mid Frequency, Treble	yes
Graphic EQ: Off / POST / PRE	yes
EQ 2
EQ	yes
MIX
Input Select	yes
ADV
Diode+ : Type, Quantity	yes
Diode- : Type Quantity	yes
Clip Type, Clip Shape	yes
Bias	yes
Bass Response	yes
Dry Level	yes
Slew Limit / Slew Rate	yes
Bit Reduce	yes
Sample Rate	yes

Mix

Unlike other effect blocks, Mix at 0% in a Drive block is not equivalent to 100% dry signal ("True Bypass").

"The models let clean through even with the mix at 100%. It depends on the diodes though as to how much clean is mixed. Our models are based on the most common versions." source

"The mix control in the Drive block controls the ratio of clean to dirty in the distortion stage. It's not the same as the standard mix control in the other effects." source

The Mix control operates prior to any tone control. This lets you mix some dry in with the distorted signal but still maintain overall tone control.

Some players like to turn down the effects’s Mix level (80% or lower) to increase transparancy and decrease buzziness.

Note that Mix is different from the Dry Level parameter in diode/opamp-based drive types (see below).

Sample Rate

Use Sample Rate Reduction to intentionally allow aliasing, for creative effects.

Bass Response and Low Cut

Firmware Ares 13 changed the functionality of Low Cut and has added the Bass Response control.

“The Drive block now features a “Bass Response” control for types based on the Rat, Tube Screamer and various derivates. In some models this is duplicated on the Basic page as it is the Bass/Voice/etc. control (and renamed accordingly). This function was previously provided by the Low Cut control. The Low Cut control is now a separate control that allows adjusting the input highpass frequency. Existing presets will automatically be updated with the new default value for the Low Cut control.”

Bit Reduce

Use Bit Reduction to intentionally lower the resolution of the signal, for creative effects.

Slew Rate / Slew Limit

This probably refers to how fast the circuit can swing its output. If the signal to be amplified is too fast, the circuit will not be able to perform properly, only amplifying signals below the slew rate limit. Poor slew rate results in high frequencies not passing through the amplifier, and thereby limiting or muting high harmonics.

The Pro Co RAT is known for its poor slew rate, because of the LM308 op-amp being used. Read this

Explanation of Slew Rate in Wikipedia:

• "In electronic musical instruments, slew circuitry or software-generated slew functions are used deliberately to provide a portamento (also called glide or lag) feature, where an initial digital value or analog control voltage is slowly transitioned to a new value over a period of time (see interpolation)"

• "Slew-induced distortion (SID or slew-rate induced distortion) is caused when an amplifier or transducer is required to change output (or displacement), i.e. slew rate, faster than it is able to do so without error. At such times any other signals may suffer considerable gain distortion, leading to intermodulation distortion. Transient intermodulation distortion may involve some degree of SID and/or distortion due to peak compression"

Explanation of Slew-induced distortion in Wikipedia:

• "Slew-induced distortion (SID or slew-rate induced distortion) is caused when an amplifier or transducer is required to change output (or displacement), i.e. slew rate, faster than it is able to do so without error. At such times any other signals may suffer considerable gain distortion, leading to intermodulation distortion.[1] Transient intermodulation distortion may involve some degree of SID and/or distortion due to peak compression"

Firmware Ares 10.01:

"Changed Drive block Slew Limit to Slew Rate and updated default value of the models. Existing presets will be updated to the new default value upon recall. Note that the parameter now controls the slew rate and lower values equal less high frequency response at high amplitudes and vice-versa (the action is reversed from the previous firmware versions)."

Graphic EQ

The 10-band Graphic EQ was added in firmware Ares.

The EQ is reset when changing the Drive type.

In firmware Ares 12 the EQ can be placed either PRE or POST distortion.

Dry Level

Even with Mix at 100%, clean level can pass through diodes. The Dry Level parameter in diode/opamp-based drive types (in firmware Ares 3.02 and later for the Axe-Fx III) determines the amount of clean level that passes through the diodes.

Release notes Ares 3.02:

"This parameter controls the amount of “dry” signal mixed with the “wet” (distorted) signal. For a Tube Screamer-based model this will default to 100% due to the topology. For other types this will default to 0. Values up to 200% are allowed. Note that the dry data is added before any tone controls and therefore is not exactly equivalent to a mix but rather replicates the behavior of analog circuits."

"If the Dry defaults to 100 then it's a Tube Screamer derivative. Tube Screamers use a non-inverting op-amp configuration with diodes in the feedback loop. This results in a transfer function that is Y = X + f(X) where f(X) is the distortion response. IOW they mix the dry signal with a distorted signal."

Drive models

BB Pre (based on: Xotic BB preamp)

An overdrive with a preamp stage. "BB" is an abbreviation of "Bluesbreaker"

Bender Fuzz (based on: Sola Sound/Vox Tone Bender)

The fuzz that Jimmy Page used to record Whole Lotta Love

Bit Crusher (custom model)

This custom model warms up a sound or deliberately degrades a signal, using bit reduction or sample rate

Blackglass B7K (based on: Darkglass Microtubes B7K)

Analog bass preamp, famous for its overdrive and transparency

Blues OD (based on: Marshall Bluesbreaker (Mk1)

Produces the mildly overdriven valve sound of the 2x12 Marshall combo amp as used by Eric Clapton in John Mayall’s Bluesbreakers

Box o'Crunch (based on: MI Audio Crunch Box V1)

Marshall-in-a-box

Compulsion Distortion LP (based on: Fulltone OCD, set to Low Peak)

The very popular "Obsessive Compulsive Drive"

Esoteric ACB (based on: Xotic AC Booster)

Thick, light-to-medium overdrive ("Almost Clean")

Esoteric RCB (based on: Xotic RC Booster v1)

"Real Clean" transparent boost pedal with gain and EQ controls

Eternal Love (based on: Lovepedal Eternity)

Clean boost, overdrive and treble booster

FAS Boost (custom model)

A custom model, designed to boost vintage amps like Plexis

FAS LED-Drive (custom model)

This custom model simulates LED clipping

FET Boost (custom model)

Gentle and smooth clipping with tone controls

FET Preamp (custom model)

Similar to the Boss FA-1 Fet Preamp, a favorite pedal of The Edge (U2)

Face Fuzz (based on: Dallas Arbiter Fuzz Face)

The fuzz that Jimi Hendrix used

Fat Rat (based on: modded Pro Co Rat)

Fuller and smoother sound than the standard Rat (see Rat Distortion)

Full OD (based on: Fulltone Full-Drive 2)

Thicker than a Tube Screamer

Hard Fuzz (custom model)

Hard-clipping, 60s-style fuzz

Heartpedal 11 (based on: Lovepedal OD11/Amp Eleven)

Sound of an overdriven tube amp

Hoodoo Drive (based on: Voodoo Lab Overdrive)

Vintage overdrive

Horizon Precision Drive (based on: Horizon Devices Precision Drive)

Sculpts metal and djent tones

Jam Ray (based on: Vemuram Jan Ray)

Boost/overdrive with a lot of headroom, recreating the tone of blackface Fender amps from the '60s

M-Zone Distortion (based on: BOSS MT-2 Metal Zone)

Get crushing metal tones from a clean amp, love it or hate it

Master Fuzz (based on: Gibson Maestro Fuzz-Tone FZ-1A)

The original fuzz, used by Keith Richards in Satisfaction

Micro Boost (based on: MXR Micro Amp)

Popular clean boost from the '80s

Mid Boost (custom model)

A custom model that boosts the middle frequencies

OD 250 (based on: reissue of the DOD Overdrive Preamp 250)

Pushes an already driven amp

Octave Distortion (based on: Tycobrahe Octavia)

Octave-up fuzz, made famous by Jimi Hendrix

PI Fuzz (based on: Electro-Harmonix Big Muff Pi Triangle)

Famous saturated fuzz

Plus Distortion (based on: MXR Distortion +)

Get more distortion from an already overdriven amp

Rat Distortion (based on: Pro Co RAT)

The famous black distortion box

SDD Preamp (based on: preamp in Korg SDD-3000)

Preamp in Korg's rackmount SDD-3000 digital delay

Shimmer Drive (custom model)

Custom model, designed to boost models of vintage non-Master amps (Plexi, Vox, Fender)

Shred Distortion (based on: Marshall Shred Master)

Marshall's distortion pedal for shredders

Suhr Riot Ge (based on: Suhr Riot)

Suhr's amp-in-a-box pedal, set to Germanium voicing

Suhr Riot LED (based on: Suhr Riot)

Version with LED voicing

Suhr Riot LED/Si (based on: Suhr Riot)

Version with hybrid LED/Silicon Diode voicing

Super OD (based on: BOSS SD-1 Super OverDrive)

The competitor to the Tube Screamer

T808 Mod (based on: modded Ibanez TS-808 Tube Screamer)

Modded Tube Screamer: more bass, more gain, more transparency

T808 OD (based on: Ibanez TS-808 Tube Screamer)

The venerable Tube Screamer

TS9DX + (based on: Ibanez TS9DX with mode set to +)

Turbo Tube Screamer in Plus-mode

Tape Distortion (custom model)

Custom model that simulates the clipping of an overdriven reel-to-reel Ampex tape deck

Timothy 1 (based on: Timmy overdrive by Paul Cochrane)

Transparent boost/overdrive pedal (blue), with the clipping mode switch set to middle position (symmetrical clipping)

Timothy 2 (based on: Timmy overdrive by Paul Cochrane)

Version with the clipping mode switch set to top position (asymmetrical clipping)

Timothy 3 (based on: Timmy overdrive by Paul Cochrane)

Version with the clipping mode switch set to bottom position (symmetrical clipping, less headroom/diodes)

Tone of Kings (based on: King of Tone by Analog Man)

Sought-after variant on Marshall's Bluesbreaker pedal

Treble Boost (based on: silicon treble booster circuit)

Silicon-based treble booster

Tube Drive 3-knob (based on: 3-knob Tube Driver)

Pedal with a 12AX7 tube inside, version with 3 knobs

Tube Drive 4-knob (based on: 4-knob Tube Driver)

Pedal with a 12AX7 tube inside, version with 4 knobs, used by Eric Johnson

Zen Master (based on: Hermida/Lovepedal Zendrive)

Most famous Dumble-in-a-box pedal, used by Robben Ford