The Axe-Fx and Axe-Fx Ultra from Fractal Audio Systems are a breakthrough in guitar effects processing. Advanced processing and unprecedented computing power offer not only the sound, but the FEEL of a real tube amp. Our proprietary algorithms accurately simulate the varying frequency response of an overdriven tube amplifier. Unlike conventional tube modelers where the frequency response is static, the Axe-Fx gives the guitarist a true dynamic experience. Cranked-amp tone and feel at any volume!