Leeneia - The new accordion has three sets of reeds or 'voices'. One is low and one high so switching between the two will achieve what Gargoyle says. This is done using the coupler switches. See here for details. You can also mix the voices to get different sounds. The one I use as default cuts in two sets of reeds to give a 'wet' sound with a slight vibrato. The middle one cuts in all the reeds. The bottom one is the lowest set only and the top switch the highest only.

Not that I am talented enough to use them to any great extent!