The 1970s loudness button wrongly assumed a flat frequency response

Evidence

In the early 1970s hi-fi manufacturers provided a “loudness” but­ ton which put in a bass and treble boost in order to flatten the Fletcher- Munson curves, and so provide a simple compensation for the reduction in hearing sensitivity at low levels. The action of this control was wrong in two important respects: n Firstly, it directly used the equal loudness contours to perform the compensation, rather than the difference between the curves at two different absolute sound pressure levels, which would be more accurate. — David Howard, Jamie Angus, coustics and Psychoacoustics, 618

Categorization

• XREF: Connects to user’s stated reading purpose — applying psychoacoustic theory; a concrete case of engineering-compensation tradeoffs.