Drive block

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The Drive block

Available on which products

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

Channels or X/Y switching

• Axe-Fx III: 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 MDProd

Drive modeling improvements

"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 (and later) for the Axe-Fx III introduced major improvements to modeling of drive pedals in the Axe-Fx III. 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."

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.

Drive models in firmware Ares 3.02 and later for the Axe-Fx III require somewhat less CPU (1-2%) than before.

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

• If the original pedal has a single Tone knob, use the Tone control in the model for authentic results.
• If the original pedal has active EQ controls (Bass / Mid / Treble), use the Bass / Mid / Treble controls in the model for authentic results.
• If the original pedal has a Volume or Level knob, it is mapped to the Level control.
• If the original pedal has a Drive or Gain knob, it is mapped to the Drive control.

"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 for the Axe-Fx III, 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.

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 the AX8, because the AX8 has a fixed input impedance setting.

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, 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.

The Axe-Fx III 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
• forum discussion

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. source

Other drives and devices

• Currently there's no Fractal Audio model of the Klon Centaur boost/overdrive pedal. Here are ways to achieve its sound:
  • Camilo Velandia matches a Klon Centaur
  • AustinBuddy suggests the following settings: Fet Boost, Drive 4.7, Tone 4.7, Level 6 - 8, Mid 0.9, Clip Type Germanium
  • Yek replicates the EHX Soul Food, a Klon clone
  • Leon Todd's AA Workhorse settings (a Klon clone)
  • Forum discussion
  • Forum discussion
  • 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

Parameters

Parameters table

Parameter	Axe-Fx III	Axe-Fx II	AX8, FX8
Type	yes
Basic – Drive	yes
Basic – Tone	yes
Basic – Mix	yes
Basic – Level	yes
Basic – Low Cut, Hit Cut	yes
Basic – Bass, Mid, Treble	yes
Expert – Clip Type	yes
Expert – Clip Hardness	yes
Expert – Bias	yes
Expert – Slew Limit	yes
Expert – Mid Frequency	yes
Expert – Bit Reduce	yes
Expert – Sample Rate	yes
EQ	yes
Input Select	yes
Dry Level	yes
Diode Type, Quantity	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 Deduction

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

Bit Reduction

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

Slew Rate

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)."

• Also: "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."

EQ

The 10-band Graphic EQ was added in firmware Ares 1.16 for the Axe-Fx III.

The EQ is reset when changing the Drive type.

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 for the Axe-Fx III:

"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 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.

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 a Plexi.

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 overdrive than a Tube Screamer.

Hard Fuzz (custom model)

Hard-clipping, 60s-style fuzz.

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

Tone of an overdriven tube amp.

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, as used by Keith Richards in Satisfaction.

Micro Boost (based on: MXR Micro Amp)

Famous clean boost from the '80s.

Mid Boost (custom model)

A custom model that boosts the middle frequencies.

Octave Distortion (based on: Tycobrahe Octavia)

Octave-up fuzz, used by Jimi Hendrix.

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

The well-known saturated fuzz.

Plus Distortion (based on: MXR Distortion +)

Designed to get more distortion from an already overdriven amp.

Rat Distortion (based on: Pro Co RAT)

The famous black box.

Ruckus Ge (based on: Suhr Riot)

Based on Suhr's modern high-gain pedal, specific voicing

Ruckus LED (based on: Suhr Riot)

Based on Suhr's modern high-gain pedal, specific voicing.

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

Preamp in Korg's rackmount SDD-3000 digital delay, used by The Edge.

Shimmer Drive (custom model)

Custom model, designed to boost models of vintage amps (Plexi, Vox).

Shred Distortion (based on: Marshall Shred Master)

Marshall's version of a distortion for shredders.

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

The competitor to the Tube Screamer.

T808 Mod (based on: modded Ibanez TS9 Tube Screamer)

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

T808 OD (based on: Ibanez TS9 Tube Screamer)

TS9DX in TS9 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 internal switch set to symmetrical clipping.

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

Transparent boost/overdrive pedal (blue), with the internal switch set to asymmetrical clipping.

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

Improved and sought-after variant on Marshall's Bluesbreaker pedal.

Treble Boost (based on: treble booster circuit)

Silicon-based treble booster.

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

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

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

Pedal with a 12AX7 tube inside, version with 4 knobs.

Zen Master (based on: Hermida/Lovepedal Zendrive)

Dumble-in-a-box.