Mono and stereo signal

From old Wiki:

Always discussion going on about this. The Axe-Fx sounds gloriously in stereo. However, that experience doesn't always translate very well to a live audience, because people seldom are in the right place to hear both sides equally well.

Use the I/O menu (> Audio) to select mono or stereo OUTPUT mode. The output mode affects the output signal only. The signal of a mono source can be transformed into a stereo signal by using certain effect blocks, or the other way around. These are the choices:

• “Stereo”: select this when going direct (no amplification) into a mixing table or when using stereo amplification
• “Sum L+R”: use this to feed a mono device. The left and right channels are summed, so both channels are sent to a single mono output. While this seems perfect for mono output, there is a caveat: summing signals can cause phase cancellation. Example 1: if a preset contains an ENH block (Stereo Enhancer), this setting will make your tone glassy, thin and hollow. Example 2: if a preset contains a delay with Phase Rev (Advanced page) switched on, all delay trails will disappear. A lot of factory presets employ either the Stereo Enhancer or the delay with Phase Rev set to on!
• “Copy L>R”: use this with a mono source. The signal of the left channel is copied to and replaces the right channel. A nice alternative for L+R Sum to avoid the phase cancellation issue. But you'll lose the right channel signal with hard-wired stereo effects such as Ping-Pong Delay. And you'll also lose cab(s) panned to the right side (when using a stereo cab or two separate cabs).

The output mode applies to Output1 only. Output2 is always stereo. So what if you want to send the FOH a stereo signal, and a (summed) mono signal to feed your monitor? Solutions:

• Do it the other way around: set Output1 to mono (monitor) and use Output2 for a stereo signal to FOH. This means that you can't use the balanced XLR outputs for FOH.
• Or: use Output1 for a stereo FOH signal. Feed your monitor thrugh Output2 using the FXL block. Force the signal into summed mono by placing a Filter or Volume of Mixer block before it, with both Pan controls set to center.

Now about the effect blocks. Flanger, Chorus and Phaser are set to mono by default. Cliff: "All the effects, except the drive and amp blocks, are fully stereo. Many of the blocks default to a dual-mono configuration to prevent phasing problems when running into a mono PA." So everything before the Amp block or a Drive block will always be summed into mono.