Thank you, Dan, and David. I get it now.
John
--- In Dan Dugan <> wrote:
>
> >>> I use 24-bit recording because it gives you extra headroom to work with.
> >> You can
> >>> record low for safety in the field and boost it in post without any loss
> >> of quality.
> >>> Now that storage is larger and cheaper, the larger file size doesn't
> >> matter much.
> >
> > I've never understood this. When you boost the level in post, why doesn't
> > that raise the noise as well as the signal?
>
> Your intuition is correct, raising the level in post raises both the signal
> and the noise.
>
> > Why isn't it better to aim for
> > the maximum possible signal level initially in order to end up with the
> > maximum s/n at the end?
>
> That was true when the major source of noise was the recording medium. But
> that is no longer true. The recording medium, digital code, now has a much
> wider dynamic range than the signals we are recording.
>
> A thought experiment. Say in a natural environment a loud bird that lands
> near my microphones makes a sound measuring 85 dBSPL. The natural background
> noise in this location is 35 dBSPL. The dynamic range of this soundscape is
> 50 dB.
>
> If I make a "hot" recording the way we used to with tape, I'd put the bird
> at, say, -5 dBFS. The ambient noise would then be recorded at a level of -55
> dBFS.
>
> But the noise level of the recording medium, 24-bit digital pulse code
> modulation (PCM), is around -138 dBFS. That means we have around 83 dB of
> unused range at the bottom of the recording.
>
> So say I back off 15 dB on my recording level and record the bird at -20
> dBFS. Now the natural ambience will be recorded at -70 dBFS.
>
> In post, I increase the gain 15 dB digitally. That raises the bird up to -5
> dBFS and the ambience to -50 dBFS. It also raises the noise of the PCM medium
> from -138 dBFS to -123 dBFS. But in the presence of -50 dB ambience that
> makes no difference at all.
>
> QED. Does that help?
>
> -Dan
>
> p.s. For simplicity I'm ignoring the difference between peak and average
> metering.
>
> dBSPL means sound pressure level. dBFS means signal level referenced to the
> maximum or clipping level of the digital code.
>
> I'm also ignoring how the recording level is adjusted, analog before the A/D
> conversion or digitally after. Another topic.
>
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