XTreme Guitar: Fractal Audio Systems Axe-Fx Ultra

December 1, 2008

To assure the highest possible audio quality, 24-bit/48kHz Cirrus Logic converters, Analog Devices op-amps, and high-quality film capacitors are employed in the analog front end and output stages—and under the hood, there’s a dual-core processor that handles more than two billion floating-point instructions per second, providing enough juice to power two complete guitar rigs simultaneously, each with multiple instances of even the most DSP-intensive effects.

Like most other devices of its type, the Axe- Fx Ultra sports a huge selection of amp and effects models—but unlike the others, it also allows you to access and fine-tune their deepest inner workings. For example, there are 49 amplifier models covering nearly every great amp you can think of, and you can tweak such component-level parameters as the center frequency for the Presence control, plate voltage/ power-amp sag and damping characteristics, and the upper and lower transformer cutoff frequencies. Parameter control for the 22 speaker cabinet simulations and 30 effects types is similarly extensive.

The Axe-Fx Ultra is designed to operate as a stand-alone device direct into a mixer or with a power amp and cabinets, connected to your amp’s input or effects loop, or as an outboard device in a pro or home studio. Accordingly, in addition to the guitar input on the front panel, it has two pairs of unbalanced stereo 1/4” inputs and outputs (the second pair double as a stereo effects loop), a pair of XLR balanced outputs, coaxial S/PDIF digital inputs and outputs, and an AES/EBU digital output via an XLR connector. MIDI In/Out/Thru jacks (the latter capable of transmitting 48-volt phantom power) and two 1/4" TRS jacks for connecting expression pedals and footswitches are also located on the rear panel. Around front, there are four knobs that control the levels of the two stereo inputs and outputs (the inputs have ladder LEDs and the outputs have clipping LEDs), 12 buttons for accessing the major functions, a medium-sized LCD, and eight buttons and a rotary encoder for parameter navigation and control. Although editing is menu-driven— and there are lots of menus—the presentation is well thought-out, with the primary parameters appearing up front and the deeper stuff available on demand.

The user interface combines an Effects Inventory with an Effects Grid. “Effects” in the inventory include pedals placed before amps, amps, cabinets, and effects placed after amps, as well as the stereo effects loop. The Effects Grid comprises four parallel signal chains in a four-row/12-column matrix, enabling you to connect up to a dozen effects “blocks” in series and/or parallel. Assembling and editing signal chains is quick and painless, with all the flexibility you could reasonably want. There are also Global Parameters that let you control the overall tone (Bass, Mid, Treble) and mix (Reverb and Effects) settings, enable/disable all power amp and cabinet emulations, and select between active and passive tone stacks.

In addition to all of those programming options, there is a Controllers and Modifiers section that allows you to control select parameters within Effects blocks either externally via MIDI commands or expression pedals and footswitches, or using one of six internal controllers. The Axe-Fx Ultra responds to MIDI program change and continuous controller messages, and individual Effects blocks within presets may be toggled off and on using a MIDI foot-controller to create a de facto pedalboard. You can also use a footswitch to step through presets sequentially (if you have, say, ten favorite presets 1-10, you can define the range so it cycles 8, 9, 10, 1, 2, etc,), or to toggle one specific effect, such as a distortion effect, on and off within a preset. Internal controllers include the usual Tempo, but also two LFOs, two ADSR Generators, an Envelope Follower, a Pitch Detector (for zeroing in on single notes when using the Whammy or other pitch effects), and even a programmable step Sequencer.

I tested the Axe-Fx Ultra in mono by plugging it directly into a Rivera Venus 6 1x12 combo, within the amp’s buffered effects loop, and straight into the power amp via the effects return. I also tested it in stereo by running its balanced and unbalanced analog, and S/PDIF digital outputs into the mic inputs of a MOTU 828mkII audio interface connected to a pair of JBL LSR28P studio monitors and a set of AKG K240 headphones. I got really good results using the amp—particularly in terms of the amp models—but to get the full impact of the more elaborate effects, stereo was definitely the way to go, either into a mixer or with two amps. A variety of guitars containing single-coil, humbucking, and P-90 pickups were used, and the Axe-Fx Ultra handled them all equally well.

The current firmware (v 5.24) includes three banks of 128 presets for a total of 384. The presets range from truly amazing—particularly some of the special effects presets—to not so hot, and many were designed for specific types of music, or to sound like a particular guitarist, so they may or may not translate to your own setup. Personally, there were only a few stock presets that worked for me as is, but many more that made fine starting points when crafting my own tones. On a less positive note, some of the presets were much louder than others, and some of the more elaborate ones were noisy. To be fair, however, I’ve never encountered a device of this type that didn’t have a lot of overblown factory presets, and while some factory presets were noisy, the Axe- Fx Ultra is exceptionally quiet overall.

Presets aside, the many individual amp and effects models themselves were all quite good—and some were simply stunning. A few of the more impressive clean amp models were the Jazz (JC-120), Class A and Top Boost (AC30), Spec. OD 1 (Dumble), Brownface (Vibroverb), Blackface (Twin), USA Clean (Mark IV), and Boutique 1 (Matchless). Outstanding models for overdrive and distortion included Tweed (Champ), Plexi 1 and Brit 800 (Marshall), Brown (EVH Marshall mod), HiPower I and II (Hiwatt), USA Lead 1 (Mark IV), and Metal (Custom). The speaker cab simulations—ranging from a 1x6 oval to various 4x12s—were all very effective. Highlights included the 4x10 Bass (Bassman), 1x12 Tweed and 1x12 Black (Deluxe), 2x12 Tweed (Twin), 4x12 20w (early British), and 4x12 Green (Greenbacks). There are also eight surprisingly realistic-sounding microphone types—including commonly used Neumanns, Shures, and a Royer—and you can even import your own custom speaker cabinet impulse responses (IRs).

In addition to getting overdrive and distortion from the amp models, you can insert one of 13 Drive blocks to get classic stompbox tones, such as Rat Fuzz, PI Fuzz, and Tube Dist. All of these sounded good, especially when matched with the right amp, but the PI Fuzz was particularly impressive, being essentially indistinguishable from an Electro- Harmonix Little Big Muff Pi in a direct A/B comparison.

The other effects are superb. The Noise Gate, Compressor, Multi-Band Compressor, and Gate/Expander, and the Parametric and Graphic Equalizers perform admirably. The flexible Delay section features 12 types— including Reverse, Quad-Series, the 40-tap Mega-Tap, and a basic 16-second Looper. The Reverb is rich and spacious, with control over myriad parameters. Harmony effects such as Pitch-Shifter, Intelligent Harmony, Crystals, two types of Whammy, and Synth offer some really great sounds, though I experienced slight tracking anomalies. The Quad Chorus and Rotary effects are exceptional, the Ring Modulator is atypically musical, and the16-stage Arpeggiator, featuring a full selection of scales, is a nice touch.

For many players the primary disconnect between digital models and actual tube amplifiers has as much to do with the way that they feel and respond to playing dynamics as it does the way they sound. When tested side-by-side with my tube amp, the Axe-Fx Ultra came frighteningly close to the genuine article, following even the most subtle shifts in dynamics, and cleaning up in the same way when rolling the guitar’s volume back. I haven’t played through the latest versions of every hardware and software amp modeler, but I’ve tried a lot of them over the years, and the Axe-Fx Ultra is easily the bestsounding and most touch-responsive one in my experience.

The Axe-Fx Ultra isn’t cheap—a slightly less-powerful “regular” Axe-Fx is also available for $500 less—but most professionalquality gear isn’t, and in this case you definitely get what you pay for (the effects alone are comparable to those found in processors costing as much or more). The unit will be of particular interest to sound designers, as it provides unprecedented routing and control options in addition to its myriad processing possibilities. I still love my tube amp, all my pedals, and my rack effects—but the Axe-Fx Ultra presents a compelling argument for consolidation, so don’t be surprised if you see me using one on my next gig.




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