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dB and gain
Hi,
As an amateurfilmer I got into a discussion regarding dB (decibels) and gain.
As far as my knowledge carries me, this is what I think explains it.You have decibels (dB) used to measure sound.
0dB is the value that represents sound where an avarage person with normal hearing, hears nothing.
In opposition where 110dB is a lot of sound that could cause hearing damage.
So far so good.
But now the discussion…
In every respectable editing program you will find an audiomixer with UV meters.
These UV meters are standard set to 0dB.
So, as far I’m with the program I assume this setting means that the imported audio is unchanged electronically meaning my sound will be imported with the same strength as it was recorded with my videocamera.
Not that my audio has 0dB if it would be measured with a audio meter.
So I think to know that there’s dB to measure sound and there’s dB to measure the electrical current to change the strength of the audio wave, as wel for example the videochip.
I know this might seem a stupid question but could someone explain what this is all about.
I get this question once in a while (I give workshops for amateurfilmers)and if I explain this, I want to explain it right.Thanks,
McLennon
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26 Replies
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Hello Freddy and welcome to the Cow Audio Forum.
dB may express sound pressure level, voltage (dBu) or power (dBm).
If Mr. Crowley stops by, I think he can give you chapter and verse.
Google is your friend. https://en.wikipedia.org/wiki/DBm
Regards,
Ty Ford
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Tnx Ty for your response.;o)
The things I know about dB and gain comes from that exact wikipedia subject.
But some people keep thinking, because anybody can write on a subject and place this on Wikipedia, that you should not always believe what’s written there. (or anywhere on the internet)
That’s why I was looking for a scond opinion in a place I KNOW there’s people who work with audio and video and also have the knowledge.
And it always sounds better if I can say that I have reference from someone in the field.So hopefully Mr. Crowley stops by and is able to give a little explanation.
Ofcource I must also admit … I don’t quite understand everything that’s written on the Wikipedia page, probably because there talking about a lot of different kinds of dB (confuses me), while I’m just looking for the difference of dB used in sound (sound pressure level) and gain in the editing software.But tnx anyway.
Greetzzzz,
Freddy McLennon
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Meters to measure level in the digital world usually show a range from -40dbfs to +20dbfs.
Digital recorders are calibrated to show a maximum input level of “0” with a standard reference level of -12dbfs or -20dbfs. What you’re calling “0” level should correctly be termed -40dbfs and lower.Eric
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Okey,
Well eric,
now I’m even more confused lol.
But hey, that’s why you guys work in the field and I’m a amateurfilmer.The question ofcource is…
Is the way audio is measured in the world, or the way audio is represented in editing software, the same?
Or is there a difference in Sound Pressure level (what we hear)and the way it’s represented in editing software (what we see on the UV meters)
I’ve been thinking there’s a difference and so I was teaching this.
dB for sound pressure level is NOT the same as dB represented on UV meters.
But There’ve been some occasions where people told me I was telling false information.
That’s what got me doubting myself if I was wright or wrong.When I’m editing, to be honest, I use the UV meters to keep my audio from going into red, all the rest I do with my ears.
But then I believe, when you’re teaching people, you should tell them these things correctly.Greetzzzzzz,
Freddy
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In an effort not to recover ground already done, can we have clarity on this use of “UV” meters. I think you mean VU meters. This stands for volume units and shows an average or mean value, therefore is no good for measuring peaks. HOwever I thinmjk it is incorrect to say that all editing software uses this. Indeed Ive never seen it on any editing software.
The full scale DB meter where the top is at o is the normal meter supplied and shows where digital clipping will occur.Peter
Post Production Dubbing Mixer
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Read this for some audio insight.
Decibels always describe a ratio between two values (in our case, it’s voltage level compared to time). More to come later…nap time now. 🙂
Wolf
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Hi Peter,
I can feel the red blush on my cheeks.
Ofcourse where talking about VU meters (shame on me)
And yes, I was incorrect about what I wrote earlier about the clipping part.
At least partly…(I think)
I work in Premiere Pro CS5.
In this program you’ll find an audiomixer.
The tracks are standard set to ‘0dB’and can be changed to max 6dB or lower dB values, while the master volume is standard set to ‘0 dB’ but here this is the maximum.
And that’s the VU meter I use to avoid clipping.
So that’s a very important point you made and so I’m very greatfull for your reply.
I’m working in Premiere for many years now, but I never knew what the difference was between the values in the tracks and the master.
Maybe I should follow some classes myself before teaching others.
But they keep asking me for these things because they like what I do in the amateurclub I’m a member of, and they think I’m on a high level.
Well, I’m on a higher level then they are, but that’s because I keep on learning thru tutorials (for example Linda.Com) and thru endless searching on the net. (and to say English isn’t my native language
,I learned that all by myself as well… god I love the internet)
Anyway, in compairisan with you guys I’m a newby.
But hey … I’m learning as we go and I want to get better.Well, I’m off to bed now.
I’m sure I’ll get the answer I’m looking for and in the meanwhile I’m greatfull for the things I learn on the side.Tnx
Greetzzzz,
Fred
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Hi Jordan,
I read the site following your link but to be honest …
this reads like chinese for me lol ;o)
(I’m terrible with mathematics, formulas and numbers)
So I’ll waite for the rest to come.
In the meantime, have a great nap.greeetzzz,
Fred
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HI again
Ofcourse where talking about VU meters.
Thought soAnd yes, I was incorrect about what I wrote earlier about the clipping part.At least partly…(I think)
I dont use Premiere Pro and never have (prob never will) but as a rule on any audio if youre driving audio so it hits into the red portion of any meter, you run a real risk of clippimng and distortion. In the old analogue days, you could distort on tape, and the onset of the audible effects was gradual as tape saturated and then had no more headroom, but digital is less forgiving, good, good, good massive distortion and no inbetween.
The tracks are standard set to ‘0dB’and can be changed to max 6dB or lower dB values, while the master volume is standard set to ‘0 dB’ but here this is the maximum.
And that’s the VU meter I use to avoid clipping.I had a quick google and yes, VERY surprisingly it does use a VU meter (at least in the CS3 video I watched) Totally unsuitable for digital systems in my opinion. As VU is only a mean value, short peaks or transients could easily clip the audio stream, and the meters would never attempt to show it if the following audio were low enough to drag the average down!
Peter
Post Production Dubbing Mixer
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Tnx for your reply Peter,
I’m working in Premiere since version 1.5 and so far I was able to avoid clipping.
But I have a great hearing that compensates my lack of technical knowledge lol :oD.But I assume on the dB issue that I’m correct in saying that Sound in real live isn’t measured in the same way as used in a studio (or audio mixer)or as represented on a videocamera (gain, +3dB, 6dB, etc.)
And that was where I got lost to start with.Greetz,
Fred
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