Weber’s Law…. well, almost… well, maybe not…

Marshall Chasin
July 13, 2011

I received this comment to an earlier blog on Weber’s Law from Dr. Brian Moore in the UK…. ‘Reducing the stereo volume from 60 dB to 55 dB may be quite noticeable, but barely noticeable if one were to reduce the stereo volume from 90 dB to 85 dB.’  … This is a mis-interpretation of Weber’s law. A reduction in level of 5 dB corresponds to a fixed ratio of intensities. So, according to Weber’s law, the change from 60-55 dB is equally detectable to the change from 90 to 85 dB. In fact, owing to the “near-miss” to Weber’s law, the change from 60 to 55 dB would be LESS noticeable than the change from 90 to 85 dB.’

Thanks for the clarification.  I have been stating Weber’s Law that way for over 30 years, but never too old to learn something new.  I actually consulted with ten of my friends (yes, I have ten friends… I pay them very well) who are audiologists and they all also had the same misinterpretation! 🙂

The bottom line is not so much whether a just noticeable difference is greater or less at lower sound levels, but that the just noticeable difference is rather large at all levels in a loud band or orchestra.  This is clearly not a Weber’s Law issue as I had initially thought, but the result is similar- one can reduce the stage level by 5 dB and it is not really noticeable by, 0r even objectionable to, the performers.

This past week was spent with over 100 of the most talented up and coming classical musicians at the National Youth Orchestra of Canada.  These are amazing musicians and some were as young as 15.  Typically the string players are the younger ones because they start at age 3 and the brass and woodwinds are older.  It takes longer to hit your stride for brass instruments.  Among the many “experiments” I did with the musicians was to have them listen to a recording of a very intense piece by Shostakovich – Josef Stalin’s favorite composer- that they had just performed.  When asked to listen for any “changes” I was able to reduce the volume by about 6 dB before anyone noticed a change.  Most, if not all, would happily play at a level that would result in only 1/4 of their damage (a 6 dB reduction) without much urging.

This was one of the results of the excellent study by Jeremy Federman and Todd Ricketts (Federman, J., & Ricketts, T. 2008. Preferred and minimum acceptable listening levels for musicians while using floor and in-ear monitors. Journal of Speech Language Hearing Research, 51(1), 147–160.).  Namely that musicians, under certain circumstances, are willing to accept a lower listening level.  In the Federman and Ricketts study, the musicians accepted this lower level (called the minimal acceptable listening level) when in ear monitors were used, rather than the stage “wedge” floor monitors.

So,… my apologies for attributing this to the Weber Law where it probably belongs under the more general heading of masking, and I am positive there are other headings but am too gun shy to travel much further. 🙂

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