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I'm trying to understand gain/volume/speaker volume and how to gain stage. I understand that gain is the input signal amplitude, and have read that we should try to keep something around -18db (another common number is -6db) for the sake of overhead for mastering.

  1. Is this number the gain input to the whole signal path, like turning a VST volume down to -18/-6 in a DAW and then you try to maintain it around -18/-6 at every dynamics and effects plugin step afterwards, or am I misunderstanding it?
  2. (Title question) If that is the case, how do you account for the audio being so quiet afterwards? Is the answer to bump up monitor/headphone volume - wouldn't that also introduce some kind of artifacts that could hinder proper mixing?
  3. Why is the decibel count negative? What do the units represent, since they can't be representing absolute negative volume?
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There are two parts to this: inside the mixing program and outside it.

Inside the program the dB measure is more or less an arbitrary level. It is used by as example volume dependent processing such as compressors. You may go above 0dB here or stay very low into a lot of minus dBs.

When the sound goes outside the mix program 0dB full scale represents Max level before distortion. It can be on your DA converter feeding the speakers or on the 24 or 16 bit files.

So as 0dB FS is distortion you want to stay below that. -6dB FS is half the signal, -12dB is 1/4 and so on. Inside the mix program it makes no difference but outside you don’t want to be below say -40dB FS assuming a 24 bit file. If you use floating point files anything goes.

One way to stay below 0dB when mixing is to turn up the loudspeaker gain a lot. Your ears may guide you there staying away from looking too hard on the meters.

Mastering is the stage where you take your mix that sounds really good in your mix environment and adapting it to sound good everywhere. If you elect to do it yourself then do whatever works for you. If you send it to someone else, agree the rules. One part of mastering is to get the levels close to zero dB FS. Here the meters are important tools.

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  • @papakias Thank you for fixing my spelling errors. My phone has a life of its own when it comes to that. I might add that the description is a simplification and assumes a "modern" mixing program. – ghellquist Dec 9 '19 at 20:17
  • Thank you for your answer! It got me thinking that there are lots of things that I am NOT doing when producing my music – papakias Dec 10 '19 at 8:21
  • actually inside the DAW -6dB is half the signal. -3dB is only half in power domain i.e. when we are talking about actual sound levels. This is confusing but it is so. In terms of headroom, -6dB is 50%. – danmcb Dec 10 '19 at 8:40
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    @danmcb You are correct. I always struggle with this. Will change answer, – ghellquist Dec 10 '19 at 22:09
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There is a lot of confusion about units here, and it stems from the fact that the way of measuring levels is different from the old analogue world and the new digital one. But they both use the same (more or less) unit, the dB (decibel). If you understand this, it will help.

The decibel is a RELATIVE unit - by itself it means nothing. It needs to be referenced to something. There are common things it can be referenced to

  • some sound pressure level (this is common when talking about actual sound levels)
  • an analogue voltage (this is used in an analogue signal chain like an old style mixer)
  • in a digital system, where signals are modeled as numbers, we reference to the BIGGEST number that our system can represent

These are some (not all) of the ways that dB's are used.

Now, dB's are basically ratios. When we talk about a positive dB number, that means we are BIGGER than the reference. When we talk about NEGATIVE dB's we are smaller.

In a digital signal chain we reference to the biggest possible number and so the numbers are always negative.

In ana analogue mixer we reference to some "nominal level" (you don't really need to worry about that, but it is typically some standardised number of volts - 0.775Vrms is common) and the actual signal could be bigger or smaller, so both positive and negative numbers are possible.

When we talk about a certain "gain stage" in a signal chain, that stage has the effect of amplifying or attenuating the signal by some amount - so that gain stage gets a number representing it's gain. Now this is a pure dB number.

And because dB's are log units - we ADD the numbers (don't worry about it - it is a math trick that just works).

So if we take an analogue signal of -60dBu (that's a real analogue signal that might come out of a microphone) and put it throigh a micamp with 70dB of gain, the output of the mic amp is +10dBu. OK so far?

Now, in a DAW, the biggest signal is 0dBFS (FS means "Full Scale", that is our biggest possible number). We want our typical average signal in our mix to be less than that. A typical number is -20dBFS.

This gives us "headroom" (think about getting your car under a low bar) of 20dB before we encounter digital clipping.

Now, if we set up a mix, let's say there are 3 signals, and we want the SUM of them to be -20dBFS - they all need to be somewhat less than that individually (how much exactly we adjust by ear when we mix).

The usual way to do this is to get EVERY signal, no matter how many to roughly that -20dBFS level, and then attanuate (i.e. apply negative gain) to each via the mix fader, so that the overall mix is also about -20FS. (This doesn't have to be exavt, but it is a guide.

What often happens is that as we build up a mix, adding more and more sources, the mix gets louder and louder until it starts to clip. Then we need to pull back all those faders by an equal amount (maybe 6dB each) so that they all stay more or less the same relative to each other, but the whole mix gets quieter.

In general your MONITORING chain (that is, headphone, power amp, speakers) should be setup to give you a sensible volume for your typical mix level (here -20FS). Changing monitoring volume should have no effect on your mix level! (but not vice versa).

I hope that helps. The key here is to more or less understand the fundamentals, so that you are able to take sensible actions when needed.

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