heh! That was kind of confusing...Do they know english when they write this sort of stuff? grin!
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Chris Smart Sent: Tuesday, June 29, 2010 11:57 AM To: [email protected] Cc: [email protected]; [email protected] Subject: [Jsonar] dBV versus dBu? Often, we run into pieces of equipment that either accept or output consumer levels (-10dBV) or so-called pro levels (+4dBu). If you're like me, you've never really understood the difference, other than pro level is hotter, i.e. louder. Also, pro usually means balanced 1/4" or XLR connectors, whereas "consumer" means RCA. Well, here's some more information on this, thanks to several people who were kind enough to answer my question in great detail. Try this link for auto-conversions: http://www.sengpielaudio.com/calculator-db-volt.htm Now, for the curious, here's the difference between these two measurements. Warning: math ahead! Generally speaking, decibels are a unit of the relative power between two signals, or between one signal and another one that's known to be at a standard level of power. In the first half of the 20th century or so, the standard signal power used to be 1 milliwatt (mW) in a 600 Ohm transmission line--thus the "m" in dBm. But audio technology isn't dominated by the telephone company any more, and we no longer use transmission lines of any kind for audio frequency signals (despite what you may see in the ads for high-priced cables--or excuse me, "interconnects"--in audiophile magazines). As a result, the normal load impedance for nearly all analog audio connections is simply "high" (or "high enough to avoid loading down the source significantly," whatever "significantly" might mean to you), and most audio level measurements have become voltage measurements. The decibel was such a useful unit that it got carried forward and transplanted into the brave, new voltage-dominated world, by assuming that whenever you compare the levels of any two signals, the load impedance on the two of them will be the same. Computationally this allows you the shortcut of leaving current out of the equation; you simply take the logarithm of the voltage ratio without computing the power levels explicitly. But then you have to multiply by 20 rather than 10 (the "deci" in decibels) because decibels are still a unit of relative power. By implication we assumed that the currents will always be proportional to the voltages when we assumed that the load impedances were some constant "high enough" value. It's a step into virtual reality in a way, but it's been the standard practice for decades now. The u in dBu usually means "unloaded" or "undetermined" and refers to impedance. The V in dBV refers to voltage. What is dBu? A logarithmic voltage ratio with a reference voltage of V0 = 0.7746 volt ? 0 dBu What is dBV? A logarithmic voltage ratio with a reference voltage of V0 = 1.0000 volt ? 0 dBV The home recording level consumer audio of -10 dBV means 0.3162 volts, that is -7.78 dBu. The studio recording level pro audio of +4 dBu means 1.228 volts. The short answer to the question is approximately 11.8 dB difference, that is, lower the volume of your pro +4dBu source by approximately 11.8dB and you're at approximately consumer levels, -10dBV. Thanks to a poster over on www.taperssection.com for the following math. -10 dBV is ca. 316 mV while +4 dBu is ca. 1.228 V. The ratio between them is ca. 3.886. The log (to the base 10) of that ratio is ca. 0.59; 20 times that is ca. 11.79; voilà. My brain hurts!!! Chris, who doesn't even remember logarithms from high school math class! _______________________________________________ Find JSonar and Sonar FAQs, articles, guides and downloads at jsonar.org. Jsonar mailing list [email protected] http://jsonar.org/mailman/listinfo/jsonar_jsonar.org _______________________________________________ Find JSonar and Sonar FAQs, articles, guides and downloads at jsonar.org. Jsonar mailing list [email protected] http://jsonar.org/mailman/listinfo/jsonar_jsonar.org
