Amp simulator

Without distortion the electric guitar probably wouldn't have had nearly the impact it has had on popular music. The Axe-Fx contains multiple distortions based on emulations of various amplifiers. As mentioned earlier the Axe-Fx is not a modeler however these emulations provide sonic characteristics very similar to the amplifier they are emulating.

One of the primary differences between the Axe-Fx and a modeling amplifier is the control philosophy. Modeling amps replicate the operation of the tone, volume, drive, etc. controls even replicating the annoying interaction among these controls. The Axe-Fx philosophy is to provide the control as a more useful tool rather than a strict replica of the original. In this regard the tone controls on the Axe-Fx are true cut/boost equalizing controls and do not interact. Because of this the controls are more powerful and are set differently than on a typical amplifier. "Diming" all the tone controls may sound great on an old tube amp but usually gives less the optimum results with the Axe-Fx.

The Axe-Fx distortion is based on a proprietary dual-stage non-linearity generator. There are two basic stages: preamplifier and power amplifier. The preamplifier stage emulates the distortion generated by classic tube preamplifiers. The power amplifier stage emulates the type of distortion generated by a tube power amplifier using our proprietary Dynamic Response TechnologyTM.

Full control over all parameters is naturally afforded allowing precise tailoring of this all-important block to your particular sonic tastes. Read the following carefully as the distortion block in the Axe-Fx is very sophisticated and a complete understanding will allow you to get the most from it. Also it is important to understand the role of the Cabinet Simulator in the overall sound. The cabinet contributes to the sound of a preset at least as much the amplifier type. If you’re not getting the exact sound you’re looking for try a different cabinet simulation. Of course there are no “rules” so there’s nothing preventing you from using a 10” blues cabinet with a high-gain amp simulation. Experimentation can lead to some unique and useful sounds.

Parameters

• TYPE - Selects the amplifier simulation. The simulations are based on classic and modern amps as well as some hybrids and completely original types that we concocted. The following types are available:
  • Tube Pre - A completely neutral, low-gain tube pre-amp simulation. Useful for warming up vocals and other instruments.
  • Jazz - Based on a Japanese solid-state amp with built-in chorus. With essentially no tone shaping this amp has a warm, midrange-thick sound that is good for jazz and fingerstyle. With the Axe-Fx’s powerful tone controls you can tweak this type to get shimmering rhythm tones as well.
  • Brownface - Based on a classic American 40-watt tube amp with built-in vibrato. Great for gutsy blues, this type breaks up nicely, especially when the Master is cranked. The original had no Mid or Presence so set these to ‘0’ for classic tone.
  • Blues - A low-to-medium gain sound great for blues. Based on a classic bass amplifier with four 10” speakers, it didn’t work so well for bass but guitar players quickly discovered it made a great blues amp. Try a treble booster in front for screaming blues work a la Albert Collins or Albert King.
  • Tweed - Based on a small, low-power, tweed-covered amp. The original had no controls other than volume. Set all tone controls to ‘0’ for authentic tone. Adjust as desired to venture into new sonic territory. Our simulation has a bit more gain than the somewhat anemic original to allow you to dial in a nice crunch. To recreate the original faithfully set the drive to about 6 and use the Master as the volume.
  • Blackface - Based on a popular, 100-watt American tube amp with two 12” speakers. This simulation captures the Normal Channel. Very similar to the Brownface model but a little more mellow. The tone-stack is also slightly different giving it just a bit different voicing.
  • Class A - A medium-gain emulation based on an early British tube amplifier. This type does not have the high-frequency emphasis like the American types and therefore has a darker sound. Try a treble boost in front for a snarling British “opera-rock” sound. This amp is notable in that it has no negative feedback around the power-amp and hence has a gritty character and less high-frequency response.
  • Top Boost - Based on the “Top Boost Mod” version of the Class A. The public yearned for a brighter amp and the designers responded by adding a treble boost circuit. At first this circuit was a retrofit but then included as standard. Our simulation captures the boosted high-frequency response and slightly reduced bass response of the original.
  • Plexi - Based on a classic British amp, the Plexi is great for crunchy rhythm work. The original was basically a copy of the 4x10 bass amp (see Blues type above) that guitar players adopted but with EL34 output tubes and other British components. Despite being essentially a copy it had a unique voice all its own. It has somewhat low preamp gain and works best with the Master and Drive both set fairly high.
  • Brit 800 - The successor to the Plexi type was the vaunted 800 series lead amplifier. Many 80’s rock hits were born using this amp and we’ve captured its tone and put it into a neat little package. This amp had EL34 output tubes, some treble peaking on the input and a little more gain than the Plexi. Like the Plexi type it likes having the Master cranked. At low Master settings the amp can be brittle but bring the Master up and the true tone of this beast comes out. Try it with any of the 4x12 cabinet types for classic rock and metal tones. Try a drive block in front for more snarl.
  • Brit 900 - The successor to the 800 series was the 900 series. This amp had basically the same power amp but a new preamp with more tone shaping, more gain, and a solid-state clipping circuit that gave it a raspier sound. This amp was designed to get more of it’s distortion from the preamp than the earlier models but you can still keep the drive low and turn up the Master for more power amp distortion.
  • Brown - Based on a modified British style head with plenty of gain and lots of mids and highs. This type captures the sound of Eddie’s early work. Crank the Master and bring the drive up until you reach sonic nirvana.
  • Boutique 1 - A medium-gain, thick, yet crisp, sound with a fair amount of power amp breakup. Based on a now-defunct amplifier that was renowned for it’s liquid tone and endless sustain. This amp had very unique tone controls and as a result a distinctive voice with a bell-like quality. The preamp gain is fairly low so crank the Master to get that gutsy crunch. Good for rhythm work in a sparse situation where fullness of tone is required.
  • Boutique 2 - Same as Boutique 1 but with more gain and a bit more high- frequency emphasis. The lead version of Boutique 1.
  • HiPower I - A medium-gain, full sound based on a famous “High Wattage” amp. These amps had a unique tone-stack and industrial quality output transformers with tremendous frequency response. Chimey with a bit of power amp breakup. Plug in your Tele and crank out some Baba O'Reilly.
  • HiPower II - Like HiPower I but using the “Brilliant” channel.
  • USA Clean - A somewhat neutral clean sound that can pushed into gentle clipping. Based on a classic California amp’s clean channel this type has a full tone with a gentle midrange dip. The power amp is punchy and clean but can be driven into light distortion if desired. Sounds best with the drive turned up fairly high.
  • USA Rhy 1 - Crunchy California rhythm sound. Effective for solo use too with the gain turned up.
  • USA Rhy 2 - Similar to USA Rhy 1 but with the “mid-boost” engaged. This effectively removes the midrange dip from the tone stack and gives a more focused sound and a bit more gain.
  • USA Lead 1 - A tight, focused, hi-gain sound great for fusion and rock leads. Based on a modern Californian lead amp that set the standard for hi-gain lead tones. With the tone-stack before the preamp tubes this type has a more liquid response than the British types where the tone-stack is after the preamp. For the classic California lead sound turn the drive up and back of the Master a bit so that most of the distortion is coming from the preamp.
  • USA Lead 2 - Similar to USA Lead I but with the “treble shift” engaged. This shifts the response of the treble control lower and gives a slightly different character to the tone. There is also a “treble peaker” on the input stage which slightly boosts the high frequencies giving this type a little more “cut”.
  • Recto 1 - Based on a diamond-plated monster that redefined hard rock and “nu-metal” this type is characterized by a big bottom and some top-end sizzle. The tone-stack location is after the preamp which is quite a departure from the earlier Californian amplifiers.
  • Recto 2 - Similar to Recto I but with a slightly different input frequency shaping circuit.
  • Solo 100 - Based on a high-gain hot-rod with a chrome chassis, this amp is noted for it’s snarling lead sound. Also great for aggressive rhythm work, this type “chugs” nicely without getting muddy. Pair it with one of the 4x12 cabinet simulations for modern rock tones.
  • Spec. OD 1 - Based on a coveted but rare lead head that was made famous by Larry Carlton and others. Another amp with a very strange tone-stack, this amp has a singing voice and is great for modern blues/fusion work. This is the clean channel.
  • Spec OD 2 - The overdrive channel of the above.
  • Euro 1 - Based on a German high-gain amp, these amps pay homage to the British amps but with lots more gain and more high-frequency emphasis. This type simulates the overdrive channel with the boost and “structure” switches off.
  • Euro 2 - As above but with the boost and structure switches on. This one has lots of gain and plenty of low-end chunk along with a crispy top-end. Great for modern metal.
  • UK GC30 - Based on a great British amp introduced in the 90’s this amp is a strange marriage of a USA style pre-distortion tone-stack, British voicing and a Class A power amp. Best for blues and lower-gain rock leads, has nice sustain qualities. Can get muddy at high drive levels, decrease the bass to compensate.
  • Buttery - Based on an 18-watt amp that gained notoriety during the late 90’s this type is a low-gain amp that relies mostly on power amplifier distortion. Try a drive in front for smooth lead sounds.
  • Metal - A custom type similar to a British type but with more gain for more grind. This simulation features quite a bit of high-frequency emphasis along with a modified British tone-stack. Capable of searing rhythm and lead tones.
  • Big Hair - Spandex, studded wrist bands, pyrotechnics and your Axe-Fx are all you'll need to relive the 80's metal scene. This custom type has a unique voicing and tone-stack that emphasizes mid frequencies without getting muddy. Now plug in and shred!
  • Hellbeast - A radical custom type with an unconventional tone-stack.
  • Supertweed - Like a vintage Tweed amplifier on steroids.
  • Fusion - A smooth, thick tone good for fusion/blues solo work.
  • FAS Clean - Combines the best features of the Blackface and the USA Clean into a hybrid clean tone that’s great for a variety of uses.
  • FAS Crunch - A hybrid British/USA crunch sound.
  • FAS Lead 1 - A neutral high gain lead with a tight midrange.
  • FAS Lead 2 - More gain and more sizzle.
  • FAS Modern - A high gain hybrid tone that’s equally suited to modern rhythm and lead work.
  • JR Blues - Based on a modern all-tube combo amp with two EL84 output tubes and a single 12” speaker. This amplifier has become an instant classic because of its gutsy tone at manageable volumes.
  • Brit Pre - Based on a rack-mount preamplifier version of the . The preamp gained notoriety for its crunchy tone and was made popular by ZZ Top.
  • Recto New - Based on the modern version of the Recto 1 and Recto 2 amps. Some minor circuit changes made this version slightly more aggressive than the originals.
  • German LD1 - Based on a very high-gain German amplifier. Lots of bass, great for aggressive, drop-tuned riff work.
• BRIGHT - Many amplifiers contain a “treble peaker” on the volume or drive control (see DRIVE below). Some amplifiers have a “bright switch” that can be used to engage or disengage the circuit. On many amps this switch is built in to the volume control as a “pull on” switch. On others the circuit is hard-wired.
  The Axe-Fx amp types default to a particular state for the bright switch. If the amp had a hard-wired treble peaker the default state is on. If the amp had no circuit at all the default state is off. You many override this state by selecting the DRIVE control and pressing ENTER. This will toggle the state of the switch. The text “BRIGHT” will appear under the control when the bright circuit is active.
  If the original amp did not have a treble peaker circuit, the bright switch uses circuit values most suited to an amp of that type. On some amps the effect may be subtle, on others, quite pronounced.
• DRIVE - Sets the preamp drive. Higher settings equal more preamp distortion. On some amplifier types the drive control has a treble peaker (like the original). When the drive is turned down the low frequencies are attenuated more than the high. As the drive is turned up the low frequencies are increased more.
  Many amplifiers have this feature and it can be heard as the drive is varied. You can use this to achieve the exact sound you’re looking for when a drive block feeds the amp. Adjust the drive control of the amp to achieve the desired amount of input treble peaking and then adjust the drive and the output level of the drive block to achieve the desired amount of distortion.
  The Drive control has 40 dB of range. At a setting of ‘0’ the gain is 40 dB below the maximum gain.
• BASS, MID, TREB - Tone controls. The tone controls in the Axe-Fx have up to twice the range of a typical amplifier. When a tone control is set to the 12:00 position (0.0 dB) it is equivalent to the simulated amplifiers control at 12:00. However, the boost cut range of the control is greater, +/- 12 dB, whereas a typical amplifier may have only +/- 6 dB or less. This allows you to get sounds, like heavily scooped mids or boosted treble, that normally wouldn't be possible.
  Also, the tone controls do not interact like a typical amplifier. So when you turn the treble control the midrange and bass are not affected. This makes dialing in a certain tone easier and quicker than with a typical tone stack. This does not affect the voicing of the simulation in that the frequency response of the original circuit is always achieved however the exact setting of the controls will be somewhat different. In general the Axe-Fx tone controls are more sensitive than a typical amp and require less extreme settings to achieve the same sound. For example, if you set the treble to full on a British hi-gain amp, the corresponding setting on the Axe-Fx is about 5.0 dB. The advantage of this philosophy is ease of use plus more flexibility and wider range of tones. Adjust the tone controls slowly and listen carefully. A 1.0 dB adjustment can make a marked difference in the tone.
  Some of the amps simulated do not have the full complement of tone controls. In those cases setting the control to 12:00 replicates the original. For example, some early amps did not have Mid controls. To capture the original faithfully simply set the control to ‘0’. Adjust the control as desired to achieve new and different tones.
  Be careful in setting the tone controls as extreme settings along with high gain can cause pickup squealing or excessive noise.
• PRES - Power amp presence control. This control boosts (or cuts) the upper frequencies from the power amp simulator by varying the negative feedback frequency response. Increasing this can help your sound “cut” through a heavy mix. This control actually has a greater range than a standard presence control. Values greater than zero behave like a typical tube amp, values less than zero actually reduce the high-frequency response even further.
  If the Damping is set to zero this control is converted to a high-shelf equalizer at the output of the power amp. This allows you to control the high-frequency response of the power amp for types that don’t have any negative feedback.
• HI CUT - This control sets the cutoff frequency of a lowpass filter at the very end of the preamp simulation. It defaults to a preset value for each amp type but can be overridden if desired. Experiment with this to fine tune your tone. For example, some of the higher gain types are characterized by fairly heavy filtering after the preamp stage but with this control you can reduce the amount of filtering and achieve a brighter tone. Conversely you gain reduce this value to achieve a darker or less brittle tone.
  If using the Axe-Fx along with a separate tube power amp you may wish to experiment with this control to achieve the desired tone as the power amp may have it’s own high-frequency filtering.
• DEPTH - This controls the effective output impedance of the power amp simulation. Higher values increase the impedance which increases the interaction of the virtual speaker with the power amp. Higher values give a fuller, looser sound, while low values can be used to achieve a more focused sound.
• DEEP - Selecting the DEPTH control and then pressing ENTER toggles the state of the DEEP switch. When the DEEP switch is active the negative feedback around the power amp is modified and the power amp will have enhanced low-frequency response adding depth and punch to the tone. This control defaults to off whenever a new amp type is chosen.
• DAMP - This controls the amount of negative feedback, or damping, in the power amp simulation. Higher values give a tighter and brighter sound but can sound harsh at very high master volume levels. Lower values give a loose and gritty sound and feel. Each amp type defaults to a its own value but you may override the default value with this control. For example, a Top Boost amp has no negative feedback and as a result a unique tonal character. You can override the default damping and dial in some negative feedback to give the power amp a more “American” sound but still retain the preamp voicing.
• SAG - This controls how dynamic the power amp simulation behaves. Higher settings simulate higher power supply impedance and thus more droop in the tube plate voltages which leads to a more compressed feel.
  This control interacts with the Master Volume control in that at low Master Volume settings this control will have little effect as the power amp is not being pushed. As the power amp is pushed and draws more virtual current from its virtual power supply the Sag control will have more effect.
  NOTE: Turning this control fully CCW defeats the power amp simulation. If you are using the Axe-Fx into an external tube power amp and cabinet you may want to set this control to zero to defeat the power amp simulation.
• MSTR VOL - This, the Master Volume, is a very important control. It determines the drive to the power amp simulator. A higher setting increases the distortion contributed by the power amp simulator. As the Master is turned up the entire character of the amp will change, just like the real thing. The tone controls will have less influence on the sound, and the sound will “bloom” more and be more touch sensitive.
  By carefully balancing Drive and Master Volume you can achieve the tone you desire. Experiment with the two to achieve your ultimate tone. Sometimes the tone you desire may be mostly preamp based and as such turn the Drive up and the Master down. Other times the tone may be mostly from the power amp so crank the Master up and back off the Drive. Amps with negative feedback (damping greater than zero) tend to have a crunchier power amp distortion and this can even get raspy if driven too hard. This is due to the negative feedback attempting to linearize the power amp. The resulting transfer function is harsher at clipping than an amp with little or no feedback. You can experiment with the damping control and master volume to achieve the desired power amp distortion timbre.
  If the Master Volume is set very high best results are usually achieved by reducing the drive control. Try setting the Master around 9 or so and then slowly bringing the drive up until the desired tone is achieved. At high Master settings less drive is usually required, especially for high-gain types.
  Amp types that are designed for preamp distortion typically sound better with lower values of this control and too high of a value can make the tone muddy or excessively noisy. This includes the USA Lead types, SOLO 100 and others. Lower gain amps such as Plexi, Brownface, and others can benefit from higher settings as this can reduce the harshness of the amp.
  If the power amp simulation is off (Sag at zero) this control then becomes a simple level control. This control has 40 dB of range. A setting of ‘5’ is therefore 20 dB less than maximum.
• LOWCUT FREQ - This control allows you to reduce the amount of low frequency content at the input to the amp simulator. This parameter defaults to a value for each type but can be overridden if desired.
• TONE FREQ - This control allows you to alter the center frequency of the tone controls. You can use this to change the character of the preamp. This parameter defaults to a value for each type but can be overridden if desired.
• XFORMER LF - This control allows you to alter the lower cutoff frequency of the “output transformer”. Increase this value to simulate an old, under-designed transformer as was common in some vintage amps. This parameter defaults to a value for each type but can be overridden if desired.
• XFORMER HF - This control allows you to alter the upper cutoff frequency of the “output transformer”. Decrease this value to simulate narrow bandwidth transformers as were common in some vintage amps. This parameter defaults to a value for each type but can be overridden if desired.
• TONE LOCATION - This control allows you to alter the location of the tone stack. “Pre” places the tone stack at the input to the amp, “post” places the stack between the preamp and power amp. This parameter defaults to a value for each type but can be overridden if desired.
• PRESENCE FREQ - This control allows you to alter the center frequency of the presence control. This parameter defaults to a value for each type but can be overridden if desired.
• LEVEL, PAN, BYP MODE - These are the standard output mixer controls.