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Re: EIN values and bits

Subject: Re: EIN values and bits
From: "John Crockett" naturalcontemplative
Date: Tue Dec 4, 2012 1:30 pm ((PST))
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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