In 1963's telephone school for newly employed wet-behind-the-ears AT&T testboardmen, we were taught 3 db as the discernible change, and the reason why circuits that "toned out" more than a half db off had to be patched out of service and adjusted spot on. The only way to get from anywhere to anywhere with a long distance circuit was to switch shorter circuits together end to end, six times a half db was 3 db.
You could plainly hear DC - Chicago - LA combos getting long and we'd make lists to pull out on midnight tours. Spent three years doing that. Until we got transistorized line bays later on that were more stable than the vaccum tube design, it was work a lot of overtime. Their maintenance schedule, the tens of thousands of of testboardmen they hired was based on the Bell Laboratories research on the matter. For that reason I may have an attachment to it, as ultimately it paid for my first house and car and put my kids through college, and is now paying retirement. If they'd said 2 dB maybe I never get hired. If one wants to dig up the research, it's found in the Bell System Technical Journal (BSTJ). This would be the stuff that everyone else refers to: 'C. F. Sacia and G. W. Beck, "The Power of Fundamental Speech Sounds," Bell Syst. Tech. J., vol. 5, pp. 395-403 (1926)' 'Harvey Fletcher and W.A. Munson, "Loudness, Its Definition, Measurement, and Calculation," Bell Syst Tech J., vol 12, issue 4 pp 377 ff.(October 1933)' Abstract: [Empirical formula for calculating loudness of any steady sound from analysis of intensity and frequency of its components developed; based on fundamental properties of hearing mechanism in such way that scale of loudness values results; in order to determine form of function representing this loudness scale, measurements were made of loudness levels....] 73, Guy. On Mon, Dec 14, 2009 at 10:07 PM, Bill Johnson <k9...@live.com> wrote: > > In technical school after being a HAM for over 9 years I learned that it took > 10Db change in level to perceive a doubling of audible signal level,,, 3 db > hard to detect. I worked on modems during the Vietnam at a site for 1 year > after tech school and all our old equipment was lab quality. I did this all > day long for 6 days a week for a year. I know and heard what I write. > > > Bill > K9YEQ > K2-#35 (2 more), KX1-#35, K3, TS2000, IC7000, etc. > > > > >> From: r...@cobi.biz >> To: elecraft@mailman.qth.net >> Date: Fri, 11 Dec 2009 14:16:54 -0800 >> Subject: Re: [Elecraft] [K3] 150 watt "boots" for 160m >> >> Quite right Bill, in an audio laboratory or perhaps in a very quiet >> telephone circuit. >> >> But radio communications is different according to what I learned in school, >> lo' these many years past. Over half a century ago most radio communications >> engineers began using 3 dB (2:1 power ratio) as the minimum change in a >> signal level that would normally be just discernable to the listener, >> considering typical band noise and QSB. That was based in actual on-the-air >> observations by a great many operators over time. >> >> When considering changing my power level, I never consider it worthwhile to >> change less than 3 dB and more typically 6 to 10 dB as the minimum worth >> bothering with (e.g. shifting from a K2/10 at 10-15 watts CW to a K2/100 was >> a just worthwhile shift). >> >> When I was much younger and more "innocent" I used to scramble for each >> little watt, exulting in running 30 watts instead of 20 watts from a 6L6, >> for example, or tweaking my 6146 rig to run 90 instead of 75 watts and >> feeling sure that made a big difference. It sure seemed to produce more >> results from calls. But, looking back over logs over time, it was clearly an >> illusion.. >> >> That's when I acquired the sign that still hangs over my desk to remind me >> that "Believing is Seeing". >> >> So I don't argue with people who want to make what is a quantifiable silly >> choice. Instead I say, "If you want to do it and you believe it's worth it, >> do it." >> >> I'm no different. After all, we humans make most of our choices based on >> emotion and then we use rational logic to justify the choice. >> >> Ron AC7AC >> >> -----Original Message----- >> >From 100 to 150, for 1.7 dB, when Bell Laboratories research (with >> huge capital investment and telephone maintenance dollars on the line) >> determined that 3 dB was the signal strength change discernment for >> most people? >> >> I'm not sure who said 3 dB was the minimum detectable by a listener but I >> believe it's incorrect. 1 dB "roughly matched the smallest attenuation >> detectable to an average listener". (see below) >> >> "The decibel originates from methods used to quantify reductions in audio >> levels in telephone circuits. These losses were originally measured in units >> of Miles of Standard Cable (MSC), where 1 MSC corresponded to the loss of >> power over a 1 mile (approximately 1.6 km) length of standard telephone >> cable at a frequency of 5000 radians per second (795.8 Hz) and roughly >> matched the smallest attenuation detectable to an average listener. Standard >> telephone cable was defined as "a cable having uniformly distributed >> resistances of 88 ohms per loop mile and uniformly distributed shunt >> capacitance of .054 microfarad per mile" (approximately 19 gauge)." >> >> http://en.wikipedia.org/wiki/Decibel#History >> >> 73, Bill >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:Elecraft@mailman.qth.net >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html > > _________________________________________________________________ > Hotmail: Trusted email with Microsoft’s powerful SPAM protection. > http://clk.atdmt.com/GBL/go/177141664/direct/01/ > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
