ashcat_lt
Well-known member
Specifically, the question you asked was:Well I'll put it back on topic.
Earlier in this post I stated that I believed the dB system wasn't linear and some people told me it was. I hear others say it's a logarithmic scale. Which is it?Or are there two different types of systems?
...which was answered in the next reply or two, and has been reiterated a number of times along the way. The context was somewhere in the middle of the discussion of just turning down all the faders by the same amount to get the master down. Aside from the fact that it's unnecessary in most modern DAWs (since you can just turn down the master fader until it avoids clipping the output), it does bring up the interesting issue of how mixing signals affects the output on the db scale. It is quite definitely not intuitive.
If you're adding (mixing) voltages, say two signals at 1V, the total will be 2V. If you turn both up by 1V, the total goes to 2 + 2 = 4V. But, when we're describing the values in db we're talking about a logarithmic expression of ratios, and they just don't add that way.
If I decide to make my own db scale - I'll call it dbLT - where 10dbLT = 1V, and then take two test tones both at 10dbLT and add them together, the total output will be 2V. If we then do the log math to convert that voltage to my scale we'll see that 2V ~ 16dbLT, a 6db increase. If we turn up both of the 10dbLT signals by 6db, we've doubled the voltage of each (to 2V each), and the output voltage is also double (4V), which is a 6db increase over the 16dbLT, so we end up with 22dbLT. If we start talking about odd numbers of tracks, and voltage adjustments which are not exact multiples of 2 (or db adjustments which are not multiples of 6), the math gets messier, but it still works the same:
If you change all of the tracks by the some given number of db, you affect exactly that many db change at the Master bus...
...unless there is something non-linear happening along the way. It will definitely fuck up things like parallel compression unless the send to those compressors is pre-fader.
Which brings us back to the fact that a modern DAW's mix "busses" don't clip internally.* The output fed from the internal buss (whether it's a physical DAC, or the "virtual output" of bouncing to fixed-point file) might clip, but in cases like the OP's, you can get away with just turning down the Master fader to avoid that. It's good practice to keep all your individual track levels down so that the master doesn't go above 0dbfs with the master fader at unity, but generally not necessary nowadays.
* I seem to be posting this info quite a bit, I need to put it somewhere readily available for cut and paste... And yes, you can run even a 64-bit float out of numbers, but you generally have to try. Internal feedback is the quickest way that I know of to accomplish this. Normal mixing of realistic numbers of real signals won't even come close. For all realistic practical purposes we can call it "impossible".
