Mr Solow labelled this all-important factor "technical change", a catch-all term for anything that yields more output from the same inputs of Labour and capital.

Productivity growth continued to be the major factor for the rest of the 1930s, accounting for about three-quarters of the growth in real per capita output that occurred between 1932 and 1939.

Often input and output levels necessary for quality recording do not match the requirements of the live mix, where stage volumes factor in to the overall room sound.