WTF is a Decibel?

hi and welcome back I got an amusing comment from a viewer yesterday to paraphrase when null testing I usually ignore any differences below minus 100 DB but we have 120 DB of dynamic range available so that leaves 20 DB one6 of one6 of our total dynamic range right how can I possibly say that's not significant I'm not going to screenshot it or quote it directly because I don't want to shame the comment at all it's a perfectly reasonable question if you don't understand how decibels work the thing is we probably all should understand how decibels work it's kind of fundamental all our volume faders and preamp gains are calibrated in decibels likewise Dynamics thresholds and EQ gains we measure our Peak levels in dbfs this really should get covered on day one of audio school so while I'm still in low effort mode Let's tackle perhaps the most important an and fundamental question so far I'm going to start by talking about a different logarithmic scale however that most musicians will probably feel more comfortable with pitch when you increase the pitch of a note by 12 semmit tones or one octave you're actually doubling the frequency when you decrease the pitch by one octave you're actually harving the frequency key Point adding and subtracting in terms of pitch is equivalent to multiplying or dividing the frequency decibels work in much the same way if you add 60b of gain what you've actually done is multiply the amplitude by two in the digital domain that means multiplying all the sample values by two in analog it means doubling the voltages and if you attenuate by 6db that means you haved all the sample values or voltages or whatever adding gain in decibels means multiplying amplitudes by a value greater than one and subtracting gain means dividing by a value greater than although in code that will probably mean multiplying by a value between zero and one instead so a few points a decibel is actually a ratio when someone says a rock concert can be as loud as 120 DB