which differed from the A-weighting curve, showing more of a peak around 6 kHz. These gave a more meaningful subjective measure of noise on audio equipment, especially on the newly invented compact cassette tape recorders with Dolby noise reduction, which were characterized by a noise spectrum dominated by the higher frequencies. BBC Research conducted listening trials in an attempt to find the best weighting curve and rectifier combination for use when measuring noise in broadcast equipment, examining the various new weighting curves in the context of noise rather than tones, confirming that they were much more valid than A-weighting when attempting to measure the subjective loudness of noise. This work also investigated the response of human hearing to tone-bursts, clicks, pink noise and a variety of other sounds that, because of their brief impulsive nature, do not give the ear and brain sufficient time to respond. The results were reported in BBC Research Report EL-17 1968/8 entitled The Assessment of Noise in Audio Frequency Circuits. The ITU-R 468 noise weighting curve, originally proposed in CCIR recommendation 468, but later adopted by numerous standards bodies (IEC, BSI, JIS, ITU) was based on the research, and incorporates a special Quasi-peak detector to account for our reduced sensitivity to short bursts and clicks. It is widely used by Broadcasters and audio professionals when they measure noise on broadcast paths and audio equipment, so they can subjectively compare equipment types with different noise spectra and characteristics. See also A-weighting Audio quality measurement Audiogram CCIR (ITU) 468 Noise Weighting dB(A) ITU-R 468 noise weighting Listener fatigue Luminosity function, the same concept in vision Mel scale Pure tone audiometry Robinson–Dadson curves Sound level meter Weighting filter Notes References Audio Engineer's Reference Book, 2nd Ed., 1999, edited Michael Talbot Smith, Focal Press. An Introduction to the Psychology of Hearing 5th ed, Brian C.J. Moore, Elsevier Press. External links ISO Standard Precise and Full-range Determination of Two-dimensional Equal Loudness Contours Fletcher–Munson is not Robinson–Dadson (PDF) Full Revision of International Standards for Equal-Loudness Level Contours (ISO 226) Test your hearing – A tool for measuring your equal-loudness contours Equal-loudness contour measurements in detail Evaluation of Loudness-level weightings and LLSEL JASA A Model of Loudness Applicable to Time-Varying Sounds AESJ Article Psychoacoustics Audio engineering ISO standards Sound Acoustics