USB

Axe-Fx II and USB in the owner's manual

• Axe-Fx II: 3.4 Connection Diagrams; 3.4.9 Axe-Fx II as a Computer Audio Interface; 3.4.11 Axe-Fx II- One Possible Big Rig; 9 Input/Output Parameters; 10.3 Status Meters; Input/Output Hardware and Parameters Guide.

Axe-Fx II USB driver for Windows and Mac

• USB drivers for Mac and Windows are required and available for download here. If the USB driver is not installed, utilities such as Axe-Edit, Fractal-Bot and Cab-Lab won't recognize the Axe-Fx II.
• When using the USB interface, there's no need for an additional audio interface. An external audio interface is required when connecting the analog Axe-Fx II outputs to a computer (not using USB).
• A MIDI interface is not required to connect the Axe-Fx II to a computer. The Axe-Fx II itself operates as an USB-to-MIDI adapter. MIDI interfaces can still be used, and editing through a MIDI interface also is still possible.
• Cliff: "The driver that we supply for OS-X computers is NOT an audio driver. It is a firmware installer. The Axe-Fx II uses a "soft" USB controller. It gets it's code from the host computer. When you turn the Axe-Fx II on it requests firmware from the host. This is superior to a hard-coded controller in that updates merely require a new host image rather than reflashing the controller."

Using the Axe-Fx II as an interface to update the MFC-101 firmware

• The Axe-Fx II can be used as an USB-to-MIDI interface to update the firmware on the MFC-101, using Fractal-Bot or a MIDI librarian. Walkthrough.
• Cliff: "The USB Adapter feature was added for simple USB-to-MIDI functionality, specifically firmware updates for the MFC-101. It is a low priority task since audio processing is the Axe-Fx's primary usage. Latency is not guaranteed. It is not intended as anything more than a no-frills, simple MIDI adapter for non-critical tasks." source

Axe-Fx II USB connection and CPU usage

• Creating an USB connection increases CPU utilization. This is by design. If a preset uses much CPU, you may run into CPU overload problems when connecting the Axe-Fx II to a computer through USB. source and source

Axe-Fx II and USB Audio

• Cliff: "The Axe-Fx II USB is 24 bits. This is 144.7 dB of dynamic range. Full-scale is about +20 dBu. So even if your guitar is -20 dBu (-40 dB re. FS) you still have over 100 dB of dynamic range. A typical single coil pickup can easily exceed -20 dBu. A humbucker can easily exceed 0 dBu. Full-scale of 20 dBu gives you a few bits of headroom in case of very hot pickups. The self noise of a guitar pickup and associated electronics limits its dynamic range to less than 100 dB typically." And: "The digital bit depth on the USB and Digital I/O exceeds both the dynamic range of the Axe-Fx itself and certainly that of any guitar. Furthermore the bit depth is sufficient to fully capture the dynamic range of a guitar while still maintaining +20 dBu as full-scale." source
• Cliff: "The hardware is incapable of doing 4x4. The only choices are 3x3 or 4x2 and Logic doesn't work with 3x3. We also had some issues with 3x3 in Windows 7 IIRC." source

Troubleshooting Axe-Fx II and USB

• High-pitched noise may be caused by a ground loop. Cliff: "The USB spec calls for grounding the cable at both ends (mistake). This can create an USB ground loop. Make sure everything is plugged into the same outlet strip." source
• When experiencing problems such as dropped connections or an Axe-Fx which freezes after connecting USB, always replace the USB cable first. Example
• Cliff: "An occasional flicker when hooked up to USB is not unusual. This is due to the screen redraw being interrupted by the USB thread." source
• Handy tip for resolving audio dropouts in your Windows DAW

Axe-Fx II and Linux

• Linux and Axe-Fx.