 By 1973, he had come up with a concept based on the early work of Steinberg and Gardner on loudness recruitment, propsing multi-channel compression to make up for the variable loss of loudness compression (recruitment).Each patient's audiogram, combined with individual testing, would determine a custom gain-map program keyed to the individual person.The multi-channel system was adapted to an indivual's hearing losses in specific frequency ranges, providing amplification where needed.