Six forward speeds and one reverse speed may be realized with minimized length and weight of the transmission by employing two single pinion planetary gear sets and a double pinion planetary gear set. A first charge air stream is introduced into the high-pressure column, where it is separated into a first oxygen-enriched liquid and a first nitrogen top gas. An air passageway includes a deflector to direct dirt into a dirt collection tray which is pivotably mounted to the housing. The method may involve encoding the level as an overload indicator, the overload indicator being conditioned on the sub-band such that the overload indicator includes enhanced layer symbols regarding the level of the measured interference amount.