I have configuration instruction stating to set an Input Audio Gain to 125 milivolts. The "updated" equipment only allows me to set this parameter to On, Off, or -1dB to -48dB. The input impedance should be 600 Ohms.
Is there a method for calculating a dB equivalent for the original 125mV setting requirement?
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milivolts to Decibel equivalent
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Our forum has been available for many years. In September 2014 we decided to switch it to read-only mode. Month after month we saw less posts with questions and answers from real people and more spam posts. We were spending more and more resources cleaning the spam until there were less them 1 legitimate message per 100 spam posts. Then we decided it's time to stop.
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milivolts to Decibel equivalent
by tvcleaner » Thu Feb 24, 2005 12:38 am
- tvcleaner
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by Guest » Sun Apr 10, 2005 1:02 am
There is a method, but you need to know the reference level. The level in decibels is a ratio (using logarithms) of a voltage or power to a reference level voltage or power. "log" below is "common" or "base 10" logarithm.
dB = 10*log (P/Pref) or 20*log(V/Vref)
These two are consistent because P = V^2/R
Common references for audio gear are dB re 1V, or db re 1mW.
Into 600 ohms, 1 mW is 0.7746 v
so 125 mV is 20*log(0.125 V/ 1 V) = =18.06 dB re 1 V
or -15.84 dB re 1 mW.
There is no way for me to guess which reference level is used; perhaps you can find it in the equipment specs. Either number will get you close.
dB = 10*log (P/Pref) or 20*log(V/Vref)
These two are consistent because P = V^2/R
Common references for audio gear are dB re 1V, or db re 1mW.
Into 600 ohms, 1 mW is 0.7746 v
so 125 mV is 20*log(0.125 V/ 1 V) = =18.06 dB re 1 V
or -15.84 dB re 1 mW.
There is no way for me to guess which reference level is used; perhaps you can find it in the equipment specs. Either number will get you close.
- Guest
More info
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