The Embellished Chords option in the Mixer controls how closely the voicings follow your chord symbols. With it off, the band plays the symbol exactly, so C△7 is C, E, G, B. With it on, the voicings add extensions for color, so C△7 might add a D or an A.

 

Jazz styles usually sound best with embellishment on, and pop styles with it off. The setting also carries through when you export a song to MIDI.

 

For more on the Mixer, see Customize your backing tracks on the iReal Pro website.