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I need help with a db question.
MUFF WIGGLER Forum Index -> Production Techniques  
Author I need help with a db question.

tompty

If i have a 70hz sine wave and a 5khz sine wave both running into my converters at -18dbfs will the final outcome be -18dbfs?

I have always wondered whether the overall db goes up with two non-clashing frequencies are summed or whether its just when frequencies overlap.


thanks!


tompty

:(


megaohm

tompty wrote:
If i have a 70hz sine wave and a 5khz sine wave both running into my converters at -18dbfs will the final outcome be -18dbfs?


It depends on when you 'look' at it.
I think your general grasp of what is going on is correct.
But two waves at different frequencies will add together at certain times depending on how their frequencies are related.


megaohm

Also, I'm a dumb ass when using dB and the like. I always refer to this page of calculators/info:

http://www.sengpielaudio.com/calculator-db-volt.htm


joshnapkins

it doesn't matter if they're not the same frequency. think of adding two sine waves of different frequency, at some points their maxima will line up perfectly and you'll get constructive interference at twice the amplitude.

and, as always, when doing any sort of math with dB make sure to convert from log scale to linear scale, do the addition/subtraction/mult/etc. and then convert back to the dB scale. i.e....

10log10(x) = -18 dB, so x = 10^(-18/10) = .016

now we add the max amplitude of each signal 0.016+0.016=0.032

now convert back to dB, 10log10(0.032) = -15dBfs


Ranxerox

Yes, frequency has nowt to do with it. As a general rule of thumb adding any two signals of the same amplitude together will result in an increase of ~3dB at the output.


tompty

brilliant!

thank you all for the helping me out with this.

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