The encoder buttons are used to set what the encoder is controlling.
When the speaker or headphone button is engaged, rotating the encoder will control the volume of that output. When moving the encoder, the volume level can be seen in the meter LEDs on the unit (as shown below) for a couple of seconds before it goes back to display the main mix level. You can mute the output by pressing the encoder, this will cause the encoder button of the output you are controlling to flash.
The iD button is a configurable hardware function button which can be used for the following purposes:
- Mono + Polarity
Any of these can be set by right clicking on the iD button icon in the mixer window and selecting the one that you want.