Muff's Modules & More

tompty · Posted: Tue Jan 18, 2011 10:31 am Post subject: I need help with a db question.

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 · Posted: Wed Jan 19, 2011 12:09 am Post subject:

megaohm

megaohm · Posted: Wed Jan 19, 2011 1:26 am Post subject:

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 · Posted: Wed Jan 19, 2011 9:12 am Post subject:

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 · Posted: Wed Jan 19, 2011 9:37 am Post subject:

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 · Posted: Wed Jan 19, 2011 10:59 am Post subject:

brilliant!

thank you all for the helping me out with this.