- 1 Processors and USB
- 2 USB-B to USB-C
- 3 USB and CPU usage
- 4 USB Adapter Mode
- 5 USB Audio
- 6 Troubleshooting USB
- 7 Linux
Processors and USB
The Axe-Fx III has a dedicated 16-core, 500 MHz USB microcontroller. USB 2.0 is used to connect the unit to a computer, to run software editors and Fractal-Bot.
Windows – Requires installing a USB driver. Requires Windows 7 SP1 or newer.
Mac – No driver required (class compliant). Requires OS X 10.6.8 for MIDI over USB, 10.9 for USB Audio.
"Still USB-over-MIDI but at least 10x faster." source
"The Axe-Fx III has a new driver . I just tested it under Reaper and was able to set the buffer size to 8 with no problems. I typically have it at 256 because I monitor directly from the output but it seems to be working fine on the lowest setting." source
"I can only get 8 to work on my fastest machine with nothing else running. 16 works on all my machines except my Macbook which I have to use 64." source
"The USB buffer size on the Axe-Fx III itself goes all the way down to 8. 256 is the highest setting and is the (conservative) default value." source
Note: the quotes above apply to the Windows driver. Macs typically require a higher buffer setting to prevent audio distortion. From the Axe-Fx III Owner's Manual:
“Set this to lower values for less latency with USB Audio, set to higher values if you are experiencing distorted audio. Stop USB audio streaming when changing this value so as to allow the buffer to reset properly. Streaming can be stopped by closing the application sending data to the Axe-Fx III or by disconnecting the USB cable."
USB performance can be monitored on the Meters page of the Home menu. The Utilities > USB menu shows the buffer performance. Normally
The USB subsystem boots instantly on power on, it doesn't depend on the DSP. The USB subsystem does need some time to settle down though. It's recommended to wait a minute or so, before launching the editor.
Support for USB Audio: 16 (8x8) channels (8 in, 8 out). Fixed at 48 kHz, 24-bit.
"The effective throughput of USB 2.0 is roughly 280 Mb/s. One channel of audio is 48000 samples/s * 24 bits/sample = 1.152 Mb/s. Theoretically you could transfer over 200 channels of audio on USB 2.0." source
USB In (from Axe-Fx III to Computer):
1+2: Output 1 (regular stereo output).
3+4: Output 2 (regular stereo output).
5+6: Input 1 (copy of signal at front/rear Instrument input, for reamping, mono).
7+8: Input 2 (copy of signal at Input 2, stereo).
USB Out (from computer to Axe-Fx III):
1+2: Routed to physical Output 1 L+R (audio from computer, added to OUT1).
3+4: Routed to physical Output 2 L+R (audio from computer, i/e/ backing tracks that can be processed separately).
5+6: Routed to the Grid via INPUT 1 block when its source is set to USB (for reamping).
7+8: Routed to the Grid via the dedicated INPUT USB block (for additional computer audio).
Firmware 2.01 adds the ability to select the source of USB Outputs 7,8 (to computer). Inputs 2-4 can be assigned to USB 7,8.
The level of the incoming USB signal from a computer or other USB device can be adjusted.
A USB audio sound source can be placed anywhere on the grid with its own dedicated block.
Incoming sound from USB Audio is mixed with the signal that comes out at Output 1. To change this, adjust the sound settings on the computer.
- Mac: see section 3 of the Owner's manual.
- Windows: use ASIO.
Axe-Fx III and iOS devices
The Axe-Fx III supports a direct connection to iOS devices, using Apple's Lightning-to-USB Camera Adapter. This means that you can use apps such as SetListMaker and BandHelper on an iPad without requiring an additional MIDI-to-USB interface (which the Axe-Fx II does require). The connection also supports USB Audio between the III and the iOS device.
To connect the Axe-Fx II through USB a driver (Windows) or firmware installer (Mac) must be downloaded to the device first from a computer. If it's not installed, utilities such as Axe-Edit, Fractal-Bot and Cab-Lab won't recognize the Axe-Fx II. Also, tablets such as an iPad do not connect to the Axe-Fx II, until the support system has been downloaded to the unit first (without power cycling).
Windows – The Axe-Fx II is an Audio Class 2.0 compliant device. A class-compliant device requires no drivers. The drivers are provided by the OS manufacturer. Audio Class 2.0 also encompasses MIDI-over-USB. Microsoft does not support Audio Class 2.0. Therefore FAS provides a driver for Windows systems. The driver for Windows contains both the firmware installer and the audio drivers.
Apple – Apple does support Audio Class 2.0, but poorly. To overcome this, you can increase the buffer size in the Axe-Fx II's I/O > Audio menu. The driver for Macs is NOT an audio driver. It is a firmware installer. The Axe-Fx II uses a "soft" USB controller. It gets its 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.
"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 its 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."
Linux – read this.
The USB connection supports USB-to-MIDI, so there's no need to use a MIDI interface in most cases. An external audio interface is required when connecting the analog Axe-Fx II outputs to a computer.
USB Audio is supported.
Lower USB Buffer Size in I/O > Audio for less latency, increase when experiencing distorted audio. You should stop USB audio streaming when changing this value so as to allow the buffer to reset properly. Streaming can be stopped by closing the application sending data to the Axe-Fx or by disconnecting the USB cable.
The meters in the Utility menu display the USB performance. Ideally the bar should be at around 50%. If the bar sinks all the way to the bottom or goes all the way to the top, then the buffer may under/overflow and the USB buffer size should be increased. The number of buffer errors that have occurred since the last buffer reset is indicated above the bar graph.
USB Level in I/O > Audio sets the level of the USB input signal sent to the main outputs. If you don't hear anything when monitoring the Axe-Fx through a computer, check this parameter. Also verify the USB/DIGI OUT setting.
USB Audio rate is fixed at 48 kHz, 24-bits.
"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
"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
AX8 and FX8
The AX8 and FX8 have an USB 2.0 type B port (host). It's fully class-compliant. USB is used to connect the unit to a computer, to run software editors and Fractal-Bot. No driver required.
USB Audio is not supported.
USB-B to USB-C
The Axe-Fx II, AX8 and FX8 have USB-B ports. Directly connecting these to a computer with a USB-C port, like a MacBook, can cause issues when using a straight USB-B to USB-C cable. To start, always connect the cable to the computer first. Sometimes an adapter (multiport) has to be placed inbetween to make things work.
The Axe-Fx III doesn't have this issue.
USB-B to USB-C cables are hard to find. Here's one from Belkin.
USB and CPU usage
Read this: CPU load.
USB Adapter Mode
The Axe-Fx II can be used as an USB-to-MIDI interface, for example to update the firmware on the MFC-101 using Fractal-Bot. This is explained in the Fractal-Bot manual.
"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
USB Adapter Mode has not been implemented in the Axe-Fx III.
Read this: USB Audio, AES and SPDIF.
Maximum length of USB cables
"The Axe-Fx III moves a LOT more data over USB than the II. The audio is 8x8 vs. 4x2 and the MIDI-Over-USB interface runs 10-100x faster. Therefore it is important that the cable adhere to specifications (5m max). source
USB ground loop
High-pitched noise may be caused by a ground loop.
"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
Screen flicker caused by USB
(Axe-Fx II) "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
USB connection problem? Check the cable
When experiencing problems such as dropped connections or worse, always replace the USB cable first. Even if the cable works with other devices, it may be faulty.
Also, use cables which are as short as possible. Cable length is a frequent cause of intermittent failures.
Distorted audio playback
When audio playback through the Axe-Fx results in distorted audio, increase the USB buffer size.
USB performance can be monitored in Utilities.
Solving audio problems on Macs
If you have issues using USB with a Mac, try cleaning all audio preferences as explained here.
The Axe-Fx II and Axe-Fx III can work as an audio and MIDI interface just as it does on Windows or OS X, although Linux is not supported officially.
- Before firmware is loaded the device will be reported as a USB device with Vendor ID 2466 and Product ID 0003.
- After the USB controller gets loaded with its firmware the Axe-Fx II will be recognized as a USB soundcard device with Vendor ID 2466 and Product ID 8003.
- For a named output when using lsusb, adequate entries for Fractal Audio Systems and the Axe-Fx II must be added to "usb.ids" (typically under /usr/share/misc/usb.ids). See source
Loading the USB firmware:
- Ubuntu 16.04 and above users can use AlbertA's PPA and install the axefx2-usb-firmware package (sudo add-apt-repository ppa:albaguirre/axe-fx2 && sudo apt update && sudo apt install axefx2-usb-firmware)
- For others, volt created an install script package that is available for download here.
Since the Axe-Fx II is an Audio Class 2.0 compliant device no additional drivers are needed. The Linux kernel already supports such devices. However, depending on your kernel version, there can be some issues:
- For systems with a kernel older than 3.10, you will need to patch clock.c in the ALSA's usb-audio kernel module (<linux>/sound/usb/clock.c). See more here.
- For systems with a kernel older than 4.10, the ALSA usb-audio driver may cause overflows or underflows at the device since there is no proper sync applied. A patch is available here. See more here.
- Ubuntu 16.04/16.10 users can use AlbertA's PPA and install the snd-usb-audio-dkms package which installs the patched kernel module (DKMS actually builds it for your running kernel and rebuilds any time there's a kernel update).
- To verify check the “USB” bar graph in Utility->Status which displays the amount of data in the USB FIFO buffer. Ideally the bar should be at around 50%. The number of buffer errors that have occurred since the last buffer reset is indicated above the bar graph - this should be zero when the driver is functioning correctly.
Threads about using Axe-Fx II with Linux:
The Axe-Fx III unlike the Axe-Fx II has the firmware built in - so there are no firmware binary blobs that have to be uploaded.
The required kernel patches have been merged in Linux v4.18. Ubuntu 18.04.2 (or derivative) has upgraded to kernel version v4.18 so the Axe-Fx III should work out of the box.
What follows are descriptions of the required patches previous to v.18:
- Due to the USB audio configuration used - asynchronous output with implicit feedback endpoints, a quirk needs to be introduced.
- The Axe-Fx III USB port enumerates immediately after being turned on - but does not respond to commands until it fully boots up, which needs a workaround in the USB audio module
Threads about using Axe-Fx III with Linux: