• We would like to remind our members that this is a privately owned, run and supported forum. You are here at the invitation and discretion of the owners. As such, rules and standards of conduct will be applied that help keep this forum functioning as the owners desire. These include, but are not limited to, removing content and even access to the forum.

    Please give yourself a refresher on the forum rules you agreed to follow when you signed up.

Type of Decibel Units Used In Level Adjustments?


Simple question, but I cannot seem to find it definitively answered: are the dB (decibel) units used for the various level settings on the AX8 root-power quantities (20 log) or power quantities (10 log)? I assume power quantities, but would like to make certain. Probably doesn't mean a lot to many people, but it is helpful for me to better understand exactly how much I am changing a signal level when I change it by +6 dB, is it twice as loud, or four times as loud?



Fractal Audio Systems
Decibels are decibels. There is no such thing as "root-power decibels".

By definition a decibel (dB) is a ratio of two powers. The formula is 10 * log10(P1/P2) where P1 and P2 are the power of two signals, respectively.

In electronics, however, we usually manipulate and measure voltage levels. It's convenient to represent the ratio of two voltage levels in dB. To do this you would need to square the voltage to get the power (since P = V^2 / R). We also assume R = 1 for convenience. With a little math you get dB = 20 * log10(V1/V2).

Therefore if we reduce the voltage level of a signal by a factor of 0.1 then the signal is now -20 dB relative to before.

dB is simply an easy-to-read logarithmic-to-linear mapping. Music, human perception, and many other things in nature typically have a logarithmic response. The decay of, for example, a cymbal is logarithmic. If you plot this on a linear axis it's hard to display because of the dynamic range. But if you use a logarithmic axis you "compress" the data into something that's easier to view. Decibels are just a widely accepted mapping. You could use any base for the log; log2, ln, etc but since we have 10 fingers log10 is nice.

The point is that X dB is X dB. If you reduce a signal by 20 dB you've reduced it's voltage to 10% of what it was previously. You also reduced it's power to 1% of what it was previously. These are the same things: 20 * log10(0.1) = 10 * log10(0.01).
Top Bottom