Always consult the official Owners Manuals first!
Pages A-C are under review. Pages D-Z have been checked and are up-to-date.
- 1 Available on which products
- 2 What are channels
- 3 Which effect blocks have channels
- 4 How to switch between channels
- 5 Audio gaps
- 6 Channels and CPU usage
- 7 Scene Ignore
- 8 Channels and modifiers
- 9 Managing channels
- 10 Resetting a channel or an entire block
- 11 Using channels to compare sounds and parameters
- 12 Videos
Available on which products
- Axe-Fx III and FM3 and FM9: yes
- Axe-Fx II: no
- MFC-101: no
- AX8: no
- FX8: no
What are channels
Read about channels in the official manuals.
The differences between presets, scenes and channels:
- A preset is like your traditional pedalboard.
- Scenes are like your traditional pedalboard at a particular moment, with effects on or off and set to a specific channel.
- CHANNELS are like the pedals on that pedalboard with its controls set in a specific way. There are 4 channels in most blocks, so 4 different sets of settings.
Most of the effect blocks in firmware Ares and later have multiple channels. Channels can be regarded as mini-presets in each block. Each channel provides a unique set of parameter values. Switching between channels is instantaneous and pretty seamless and can be done manually (on the hardware or with a foot controller) or automatically when changing scenes. Channels can also be switched via MIDI for applications requiring automation.
Channels provide quick and easy switching between sounds without the unwanted side-effects of preset changes (due to grid reordering). For example, set the Amp block so that Channel A is a “Deluxe Verb” model, Channel B is a “Plexi”, Channel C is a “Recto” and Channel D is “FAS Modern”. Then change channels almost instantly at the touch of a button.
Channel-switching is the successor of X/Y switching, a feature of the Axe-Fx II, AX8, FX8 (and MFC-101).
"Channels are the cat's sphincter. Many blocks, including the amp block, have four channels. Channels switch instantly." 
"Channels save all settings for a block. A channel is like a preset within a block." 
"Channels can be thought of as a preset for an individual block. For example, you can think of the Delay block as being a stand-alone delay pedal (or rackmount processor) with four presets. Scenes store the bypass state and channel for each block. By using scenes and channels you can use a single preset for an entire song, an entire set or even the entire show. Since the routing doesn't need to change things switch fast and smooth. When switching presets the processor has to assume the routing might have changed and therefore has to clear all the buffers, mute the audio, etc. which takes time and interrupts the audio." 
The Axe-Fx III was designed so that single preset can be thought of as an entire rack full of processors. Each virtual processor has up to four presets. So if you were trying to do spillover in a rack you would use two reverb processors. 
"The Control block has four channels." 
Which effect blocks have channels
The list below applies to the Axe-Fx III.
The effect blocks on the FM3 and FM9 have the same number of channels as on the Axe-Fx III.
There's a single exception: the Multiplexer has 6 channels on the Axe-Fx III and FM9, and 4 channels on the FM3.
And read this:
How to switch between channels
To switch between the channels of an effect block, use:
- the hardware GUI
- the software editor
- FC-6 or FC-12 controller
- MIDI: assign a MIDI CC in the MIDI/Remote menu (Axe-Fx III, FM3, FM9 only), and specify a value to select a specific channel:
- 0 = A
- 1 = B
- 2 = C
- 3 = D
Prior to firmware 23 for the Axe-Fx, switching channels on an Amp block and some other effect blocks would cause a short gap in the sound. There's none now, depending on the global parameter Gapless Changes. Even with the global parameter disabled, channel switching speed has been improved in firmware 23 and later, in particular Amp and Cabinet block channel switching times.
Also read this:
Fractal Audio: 
"There are caveats:
- If presets are using a lot of CPU then the gapless switching may not work as there is not enough CPU available.
- If presets are "stale" (saved under an older revision) then gapless switching may not work until the presets are saved. This is because the preset is being updated during the switchover.
- If you switch presets rapidly you may get a gap because a lot of stuff goes on in the background after switching presets to get ready for the next preset change. If you switch before these background tasks are completed then you'll get a gap. It can take a few seconds for the tasks to complete."
Channels and CPU usage
CPU usage is calculated based on the currently selected channel of an effect. When switching channels, CPU usage may change.
Channels and modifiers
If an internal or external controller is assigned as a source to a parameter, you can choose between applying it to all channels of that block, or to just a single channel.
Note: a parameter allows only one modifier, not multiple.
On the hardware, channel settings can be copied-and-pasted within the same block (Layout > Tools), or swapped.
To copy channels between blocks and to/from other presets, use the software editor.
Resetting a channel or an entire block
Resetting a block defaults the parameters of the current channel. It does not change the settings of other channels.
To reset all channels of the block, switch to the other channels and repeat the process, or use the software editor to reset the entire block in one go.
Read this: Resetting blocks
Using channels to compare sounds and parameters
Channels offer an easy way to compare sounds when tweaking. They also allow you to quickly detect non-default settings by resetting one channel to default settings and then comparing the channels.
An alternative approach to comparing sounds is saving a preset as a Snapshot in the editor. Select Revert to get the original sound back. Then drag and drop the Snapshot file into the editor.