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I've read a lot about gain when you have multiple inputs, it's best in a digital setup to keep it well under 0.

I can't find anything about a single input though, which is what I'm recording for some instructional videos.

My mic is only giving me an average of -30dB, much lower than the ideal -18dB. So the volume or gain need increasing.

If I only have a single input, is there any difference between boosting gain when recording, and just increasing the volume in my editing program (DaVinci Resolve)?

Is 1 better, or how are they different?

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  • I'm really wondering where this -18 dBFS number showed up as the optimum value for a recorded signal level. Both you and Ian Bell refer to it. Would you care to elaborate a bit?
    – ZaellixA
    Feb 2 at 0:25

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Gain is more technical and can be discussed and measured in specific terms. Volume isn't really an appropriate term in mixing. It relates more to final amplification. There's no good way to relate one volume level to another. Sound pressure level is what's usually meant when people speak of volume.

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  • OK let me rephrase. Is there any difference to the quality of the output whether I raise gain on the input of a single source in software (OBS), or increase the ‘volume’ in the clip in DaVinci Resolve?
    – niico
    Sep 8, 2020 at 9:08
  • As @IanBell points out, early gain is better than later gain, because late-stage gain amplifies both the original signal and any added noise. Within clipping limits, you're better served by higher signal levels throughout the chain, because any later reduction will also reduce noise.
    – Jim Mack
    Sep 8, 2020 at 16:12
  • Thanks. I'll rephrase what you said to see if I understand. You're saying it's better to get more signal and more noise at the start, because you can filter the noise later and you're left with more signal?
    – niico
    Sep 10, 2020 at 6:11
  • @niico - It's not about filtering, just levels. If your end goal is to have a signal of level X, starting with level XXX, then any noise picked up along the way will be reduced by 2/3 when you lower the original signal (+noise) from XXX to X. If you start with X, intending to get to XXX, then any noise introduced will be increased by a factor of 3 when you raise the signal (+noise) from X to XXX
    – Jim Mack
    Sep 10, 2020 at 15:16
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Once you record, the achievable signal to noise ratio becomes fixed. So, if you increase the volume on playback you also increase the noise. In general it is better to increase the gain of the mic pre so the recorded level is -18dBFS in order to maximise the signal to noise ratio.

Cheers

Ian

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  • Thanks. I'm increasing gain in OBS software though, wouldn't that also increase noise? I can't get my lav mic (Rode Smartlav+) to get to -18dBFS by itself, I need to add a gain filter in OBS to get there. Is it OK that my lav doesn't get there by itself? Is it normal / OK to increase gain in software?
    – niico
    Sep 8, 2020 at 9:09
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    Any gain change in software will not improve the signal to noise ratio; it will simply raise the signal and the noise by the same amount. Gain usually refers to the analogue part of the signal chain. What input interface are you using?
    – Ian Bell
    Sep 9, 2020 at 11:38
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It all boils down to what is called gain structure. You would like to make all pieces of equipment in your signal's chain to peak at the same time. This means they will peak for the same input signal altogether.

Assuming all pieces are linear (which is not the case but if you have favourite level regions for each piece of equipment you can set that as your target instead of the maximum) then, by making sure each piece peaks for the same signal it means that you have set your equipment in such a way that each and every piece uses all its available dynamic range, effectively setting the signal as far from the inherent noise of each machine as possible. This translates to maximising the Signal-to-Noise Ratio (SNR) of your setup.

Now, if you have already recorded the signal and try to apply digital gain, you most probably end up just bringing the recorded signal, along with all noise included higher in the digital dynamic range regime of your system. Most often than not, gain and level perform the same operation to the signal, multiplying, that is. The term may change from gain to level based on the stage this happens and from manufacturer to manufacturer. Nowadays, some good manufacturers may perform more complicated operations on the signal to avoid loss of numerical accuracy when attenuating signals but this has nothing to do with noise reduction.

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