1. The ATH is the lowest of the equal-loudness contours . 2. Fletcher and Munson first measured equal-loudness contours using headphones ( 1933 ). 3. This describes an equal-loudness contour circuit. 4. These effects must be considered when comparing results of various attempts to measure equal-loudness contours . 5. Audible quantization error is reduced by noise shaping the error according to an equal-loudness contour . 6. In 2003, was revised as equal-loudness contour using data collected from 12 international studies. 7. The lowest equal-loudness contour represents the quietest audible tone the " absolute threshold of hearing ". 8. The unit of measurement for loudness levels is the phon, and is arrived at by reference to equal-loudness contours . 9. The equal-loudness contours are a way of mapping the dB SPL of a pure tone to the perceived loudness level ( LN ) in phons. 10. A-weighting began with work by Fletcher and Munson which resulted in their publication, in 1933, of a set of equal-loudness contours .
