Fractal Audio's Real-time Guitar Pre-amp Is Routable and Programmable with TigerSHARC®

Mother Nature is the perfect designer, composing complex real-world patterns like those found in snowflakes, clouds and networks of rivers. These naturally occurring, irregular designs are called "fractals," repeating patterns that can possess nearly infinite detail. These patterns cannot be explained by classical geometry, and they are easily found in nature.

Fractal Audio Systems, a designer and manufacturer of guitar pre-amp and audio processing equipment, is also a firm believer in the complexity of Mother Nature. The proprietary natural-processing algorithms that replicate patterns occurring in nature is both the main reason for Fractal Audio's unique sound and the origin of the company's name. Using their unique and proprietary algorithms, Fractal Audio Systems is able to achieve smooth, "analog" sound from an all-digital device.

When Fractal Audio was designing its Axe-Fx™ guitar pre-amp and effects processor, the company wanted to provide effects that sound as they were originally intended and with utmost quality. To do so, Fractal Audio needed a DSP with enough raw computing power and floating-point performance to process their complex algorithms.

Fractal Audio chose an Analog Devices, Inc. (ADI) ADSP-TS203S TigerSHARC® processor — a 500 MHz chip with 4Mb of on-chip DRAM. Fractal Audio president Cliff Chase says that the unparalleled performance of the TigerSHARC processor has enabled the Axe-FX to simulate traditional analog effects and tube amplifiers with a high level of realism and sound quality.

Stockroom of Effects
Fractal Audio's Axe-Fx is a fully routable, fully programmable, real-time guitar pre-amp and multi-effects processor. Its advanced processing algorithms and unprecedented computing power offer not only the sound, but also the feel of a real tube amp, accurately simulating the dynamic frequency response of an overdriven tube amplifier. Along with this is a virtual studio full of classic and modern audio effects including reverb, chorus, flanger, phaser, rotary simulator, pitch shifter, and many, many more (see box). All the effects use the company's proprietary "natural" algorithms, which achieve an "organic" sound not found in other products.

Axe-FX Effects

Noise gate
Graphic equalizer
Parametric equalizer
Amplifier emulator
Cabinet emulator
Rotary cabinet
Formant synthesizer
Quad-tap delay filter
Pitch shifter
Drive stereo enhancer
Effects loop

Working on the principle of an "effects inventory" (a virtual stockroom of effects), effects are placed on a routing grid where they are connected to other effects and controllers, and then edited and mixed down. The Axe-Fx allows for extensive programming of each of its effects parameters, which can also be controlled in real-time (through an expression pedal/footswitch or a MIDI). The device's huge internal memory allows for the storage of 384 patches.

The key to the Axe-Fx's unique sound is the company's proprietary natural processing algorithms (as previously mentioned), which replicate patterns that occur in nature. "In order to bring ultimate realism and sound quality to the Axe-FX processor, large amounts of floating-point DSP horsepower is necessary," said Chase. "The TigerSHARC line of processors offered the best combination of price and performance in terms of MFLOPS (Million-Floating Point Operations Per Second) per dollar."

Superior Floating-Point Performance
Fractal's Chase just can't say enough about the superior floating-point performance and price/performance of TigerSHARC for modeling the intricacies of a tube power amplifier in his market. "Accurately modeling the dynamic behavior of a tube-amp requires an immense amount of computational power. We achieved our goals at a price point supported by the musical instrument market because of the TigerSHARC's industry-leading floating-point performance per dollar," said Chase.

The ADSP-TS203S TigerSHARC processor is an ultra high-performance, static super-scalar processor optimized for large signal processing tasks. It combines very wide memory widths with dual computation blocks, supporting floating-point (IEEE 32-bit and extended precision 40-bit) and fixed-point (8-, 16-, 32- and 64-bit) processing. Operating at 500 MHz, the ADSP-TS203S processor's core has a 2.0 ns instruction cycle time.

Using its single-instruction, multiple-data (SIMD) features, the ADSP-TS203S processor can perform four billion 40-bit MACs or one billion, 80-bit MACs per second. The processor's dual compute blocks can execute computations independently or together as a SIMD engine. The architecture balances extraordinary compute capacity with large memory and I/O bandwidth realizing the highest levels of sustained performance.

"The unparalleled performance of the TigerSHARC processor has enabled the Axe-FX to simulate traditional analog effects and tube amplifiers with a high level of realism and sound quality."
Cliff Chase    
Fractal Audio

For musical effects like reverb and delay, Fractal Audio needed large amounts of both on-chip and off-chip memory. "High-quality reverb requires large amounts of internal and external memory for sample delay lines," said Chase. "The large quantity of embedded DRAM on the TigerSHARC and the flexible SDRAM interface made this very easy to implement." The ADSP-TS203S TigerSHARC processor comes with 4Mb of on- chip DRAM memory. The processor also comes with an external port that provides an interface to an off-chip SDRAM controller and standard SDRAM memory.

For tools, Fractal Audio leveraged ADI's CROSSCORE software and hardware development tools, including the HPPCI-ICE high-performance PCI-based in-circuit emulator and VisualDSP++ Integrated Development and Debugging Environment (IDDE).

The emulator provides state-of-the-art emulation for ADI's JTAG DSPs. It offers code download at speeds of up to 2.2 MB/second, allowing applications to be tested in a fraction of the time by gathering data samples 10 times faster than before. VisualDSP++ lets programmers develop and debug an application. The environment includes an easy to use assembler, which is based on an algebraic syntax, an archiver (librarian/library builder), a linker, a loader, a cycle-accurate instruction-level simulator, a C/C++ compiler, and a C/C++ runtime library that includes DSP and mathematical functions. "The VisualDSP++ tools and the emulator ease the development effort and the integrated environment enhances productivity," said Chase.

Fractal Audio's innovative "research oriented" approach to modeling the signal chain of the traditional guitar amplifier will continue to become more sophisticated and will perhaps even converge on the infinite resolution of the real world. And with newer, faster versions of ADI's TigerSHARC processors on board, future effects processors from Fractal Audio may just give Mother Nature a run for her money.

For more information on Fractal Audio Systems, please visit Fractal Audio Systems.

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